The camera's position also means you have to turn the phone upside down every time you want to take a photo, and wait for the gyroscope and OS to catch up with the new orientation before you press the shutter button. Alternatively, you have to grip the phone by the edges, using just your fingertips, which doesn't always feel quite right either.

If you can get past this early awkwardness, however, you'll quickly come to like the stock Android camera app, which -- like the rest of YotaPhone's operating system -- has been left largely unaltered. It's full of speedy little shortcuts, like switching between the camera and the gallery by swiping to the left or right; and tapping and holding anywhere on the screen not only to set focus and exposure but also to bring up a radial menu for quick access to settings. The only onscreen camera buttons you need to worry about are the shutter release and a mode button to quickly switch between still photography, video and panorama. It all takes a bit of getting used to, if you're new to stock Android, but it's uncluttered and intelligent.

The YotaPhone's 13-megapixel image output is of decent quality for an off-the-shelf camera module, which is a polite way of saying there's little to report in terms of either flaws or bonuses. JPEG compression isn't too harsh, leaving around 3.8MB of data in an average still, and the multi-exposure HDR mode usually provides images with minimal blur from handshake. Video quality is equally competent, with fast and sensible automatic adjustments, and with gentle enough compression to cope with detail and motion. The only weakness there is with the audio, which occasionally pops and also has excessive noise reduction that can make voices sound tinny. Lastly, the front-facing camera is passable, but too low-res and too highly compressed to use for anything but video chat -- output images are 1,280 x 720 and tend to be less than 200KB in size.

Software

It's in the software department that the YotaPhone comes alive. This is also where it dies on its feet. The predicament is simple: There's enough pre-installed software on this phone to demonstrate that the second E Ink screen has real potential, but there's not nearly enough support for this display to make it useful right now.

Back when the YotaPhone was still in the prototype stage, we pressed its creators over the need to somehow support Kindle and other e-reading apps. We were told that this support would come, by means of a workaround that would allow the user to trigger page-turns using swipe gestures, regardless of whether Amazon's Kindle app ever officially supported the YotaPhone's E Ink panel. This idea hasn't made it through to this build, and that's a huge limitation.

As it stands, the only way to read e-books on the YotaPhone's E Ink screen is by means of Yota's pre-installed app, Bookmate, which seems to only offer a handful of out-of-copyright items in English. There's a subscription model that might help users in Russia to access a wider and more recent range of content, but it's not available in the UK. As a result, the phone is currently useless for e-book reading -- at least until someone can find a workaround to trigger those page-turns as Yota Devices originally envisaged. (See the end of this article for a quick update on the e-book situation.)

In any case, let's take a step back and look at how you actually get information onto the rear screen.

The first method is by mirroring the LCD to the E Ink, by means of a two-finger swipe downwards on the LCD side. This is mirroring of the dumbest sort -- you're effectively just creating a screen grab and then displaying the JPEG on the rear panel. This might have a few uses -- if you need to keep a boarding pass or some detailed info up on the screen for a while -- but those situations are rare.

The second method of sharing displays is much smarter. Apps that have been built or customized for the YotaPhone have a button in the top-right corner of the screen that triggers some function on the rear panel -- and instead of just a static image, this function can be dynamic and interactive. Equally, the YotaPhone's customized version of Android 4.2 is able to send some notifications across automatically. The best way to illustrate this is by going through the three main pre-installed apps and functions that will be of use to an English-speaking audience.

Notifications

When you get an email, text, weather alert or any other notification, the YotaPhone gives the usual audio alert and displays a summary of the notification on the rear panel. You then swipe to remove these notifications one by one.

Depending on your chosen privacy settings, you can decide how detailed a notification summary is. It can just be the number of alerts of a certain type that are awaiting your attention, or it can include sender details and the first line of content. You can also choose to treat notifications differently depending on who the sender is, by adding certain contacts to a list of people whose notifications are treated as private and kept off the permanent rear display.

Calendar and Notes

You need to think carefully about the issue of privacy, because people do notice what's written on the back of your phone -- and because the phone is so different, they often can't help but stare. This applies to notifications, but it's perhaps even more important with the "Organizer" app, especially if you have colleague's appointments shown in your Google calendar.

If you can get around the privacy issue, either by keeping the phone in your pocket or just not caring about what people see on the back, then you might find it incredibly important to have an always-on agenda displayed on your phone. And this agenda is up-to-date, too: If someone adds an appointment to your calendar, it'll show up on the E Ink panel automatically after a short delay.

The Organizer app is okay, and it offers basic control over which calendars to follow, but it can't compete with calendar apps favored by power users. For example, there's little ability to display to-do lists or notes alongside appointments -- they can only be shown separately, by means of a Notes app, which should really have been integrated into Organizer. This is the problem with Yota's reliance on customized apps -- they'll just never be up to the level of what's available in the Google Play Store.

Maps

The YotaPhone comes with a pre-installed mapping app called MapsWithMe, which offers country-specific map downloads and seems to be relatively reliable -- at least for the small part of London geography that we tested it with. You can set pins, and home in on your position, and then hit the "Flip" button to send the map to the always-on display. From there, you can use swipe gestures to zoom in or out of the map. Unfortunately, the rate at which your position refreshes is way too slow for driving, but it's handy enough at a walking speed.

Social networks and RSS

This app can be configured to send tweets, Facebook updates and RSS feeds to your rear display. Strangely, these notifications don't auto-update; you have to swipe to unlock the screen and then swipe again or hit the volume rocker to see the latest messages. Another limitation is that you can't show different types of messages at the same time. This is no match for HTC's BlinkFeed, for example, which displays tweets alongside Facebook updates and everything else. In fact, it's hard to see how this could be called a "hub" at all.

Performance and battery life

We encountered a few bugs with our review unit. It crashed on occasion, for no obvious reason, and had to be restarted. Sometimes the lock screen was unresponsive until the display was switched off and then on again. But on the other hand, the phone's cellular functions, WiFi, GPS and compass all seem to be reliable. The phone's bands aren't suited to the US, but there's healthy support for 3G and LTE in the UK and Europe, including the key 800MHz, 1,800MHz and 2,600MHz LTE bands. On Vodafone's LTE network in London, we had no trouble getting beyond 10 Mbps down and up with a couple bars of reception, and the phone was good at holding onto a weak LTE signal.

YotaPhone HTC One mini Sony Xperia Z1 Quadrant 2.0 6,704 5,663 22,125 Vellamo 2.0 1,897 2,118 2,891 AnTuTu 3.2 17,935 10,048 29,377 SunSpider 1.0 (ms) 1,220 1,442 804 GFXBenchmark T-Rex 2.7 HD Offscreen (fps) 16 15 N/A CF-Bench 9,800 6,543 31,702 Battery run-down test 7:05 6:00 12:34 SunSpider: lower scores are better

In terms of the main processor, we're looking at the Snapdragon S4 Pro of yesteryear. Yota Devices originally said that the YotaPhone would come with a current-gen SoC, so we're slightly disappointed not to get a Snapdragon 600 or even 800 in the final build. The S4 Pro's performance isn't bad by any stretch, with app load times and general navigation fluidity that is noticeably better than Snapdragion 400 phones like the HTC One mini, and not too far off Snapdragon 600 handsets like the Galaxy S 4 and HTC One. In fact, in terms of gaming performance as measured by 3D Mark, the YotaPhone was able to marginally beat the more recent HTC One Max, with 6987 points. Then again, a true flagship like the Sony Xperia Z1 trounces the whole lot, while also revealing that other big issue with the YotaPhone's older processor: poor power efficiency.

With the latest chips, we're used to seeing more than nine hours in our standard battery rundown test, rising to 12 or more hours on some flagship phones. The YotaPhone barely survived seven hours in the same test, on HSPA+ rather than LTE, and its real-world stamina was even worse. On a day with extremely light use, we'd barely make it to 11PM with any battery left. Notching up the usage slightly, by throwing in music playback over headphones, Netflix and other activities, and we struggled to make it until 8PM. It's hard to forgive this when we're reviewing a handset that is being sold on the basis of longer battery life.

Wrap-up

This is an unhappy conclusion to reach, given all the technical challenges that Yota Devices has overcome in the past couple of years. But it's unavoidable: The YotaPhone isn't yet ready to deliver on its dual-screen promise due to various issues ranging from poor build quality to short battery life and, most importantly, an inability to make use of its rear E Ink panel except in a very limited selection of pre-installed apps. Without support for our favorite e-book and magazine platforms, or for Spotify and other streaming apps, or transport updates and Google Now (which we're told is coming soon), there just isn't much reason for us to flip the phone over.

What's needed is a big push on the software front. Not just in terms of stimulating third-party app developers to take the YotaPhone seriously, but also by reducing the phone's reliance on those developers in the first place. This might happen through better mirroring of the LCD onto the E Ink side, rather than the stagnant screengrab-mirroring we have now, alongside some kind of mapping from swipe gestures to standard navigation functions (forwards, backwards, play, pause, et cetera).

This lack of support could potentially be solved within this generation of the product, through some major software updates, but we wouldn't rush out to buy the YotaPhone unless and until that happens. The other option is to wait for a complete hardware revision, in the hope that it'll bring a full touch-sensitive E Ink panel or some other solution. Either way, with all the expertise Yota Devices has gained in putting this type of display into a phone, there's a much better chance that this type of hybrid handset will one day be successful.

Update: With regards to e-book platform support on the E Ink display, Bookmate says it's working on deals with English-language publishers in order to bring hundreds, or potentially "thousands" of copyrighted titles by mid-2014. We're also told that the popular free Android app, FBReader, will be made to work on the YotaPhone's rear screen any day now, bringing the ability to read non-encrypted .epub and .mobi e-books, as well as .doc and .rtf files. Meanwhile, Yota Devices says it's "discussing potential cooperation" with Amazon in the hope of getting support for Kindle books. We'll continue to cover these developments as and when they happen.