What if you could add a second screen to your iPhone? And what if that screen — on the back of the phone — could let you see favorite photos, your calendar, news and weather alerts and other information, all without unlocking the phone or draining its battery?

This week, I reviewed just such a product. It’s called PopSlate, and it’s a case for the iPhone 6 with a built-in screen powered by its own battery. It costs $129, and comes from a small Silicon Valley company of the same name which has been developing it for several years. The case went on sale on the company’s website late last month.

PopSlate’s rear screen is a gray-scale E-Ink display, similar to that on the Kindle. It uses very little power, and can constantly display an image until you decide to rotate to another using a small button built into the side of the case. It can hold up to eight different images, and the company says its tiny internal battery lasts up to a week.

The case — which is also designed to protect the iPhone — is controlled by a free app, which allows you to send your own images to the screen, or those posted to PopSlate’s social network by other users, or photos from Instagram. The company calls this process “popping.”

In my tests, the PopSlate worked as advertised, without bugs. And I could see its potential for sparing users from digging around on the phone for information, or using up the phone’s battery. There’s a lot to be said for an accessory that makes pictures or key information available by just flipping the phone over.

If nothing else, it’s a cool form of self-expression that features multiple designs you can change at the press of a button.

But the product has some significant downsides, at least in its initial release. Right now, all it can do is display images, not information or alerts. For instance, if you want to see today’s calendar, you have to tediously call it up on the phone, take a screenshot, and then publish, or “pop” that screenshot to the rear screen using the PopSlate app.

Automatic feeds of news headlines, calendars and other information won’t be available until later in the year, when the company plans to release a developer’s kit and induce third parties to use it. The company pledges to update its software as these new information types and other new features become available.

Meanwhile, as an interim step, PopSlate hopes in a couple of weeks to be compatible with a tool called IFTTT, or If This Then That. This is a website and app that allows users to create “recipes” of automated actions — for instance, if a new story on your favorite team appears, you can email it to yourself.

I got an early look at this PopSlate integration with IFTTT, and it did work. I was able to automatically push to the PopSlate screen all new photos I took, or tomorrow’s weather forecast, or headlines from the New York Times and ESPN.

But PopSlate won’t reach its full potential until it can directly handle information and image feeds you want without relying on IFTTT.

The rigid case is made of thin plastic, but it’s sturdy. It’s easy to put on and take off, by just popping it on and off. Like many cases, it adds bulk and thickness to the slender phone, though I was still able to comfortably fit the encased phone in the front pocket of my jeans. In my tests, it protected the iPhone in drops of a few feet onto a hard surface.

The rear screen itself is made of a thin, flexible plastic, and it’s recessed. So the company says it’s highly unlikely to suffer damage.

In addition, I found the PopSlate app easy to use, and the process of sending an image to the screen was quick. The case is linked to the iPhone, and therefore to the PopSlate app, via Bluetooth, a connection that didn’t have any discernible impact on the iPhone’s battery.

There are some other downsides. Your favorite images can only be seen in gray-scale, not in color. The screen doesn’t respond to touch, and the content it displays can’t be scrolled or zoomed in or out. If a news item includes a link, it can’t be opened.

The PopSlate company concedes all of this, but says the whole point is just to be able to glance at pictures and information, not replicate all the functions of the iPhone. In addition, the company has plans later in the year to introduce a feature that will allow you to long-press the side button and open up any link on the PopSlate screen in the iPhone’s own Web browser, should you want to explore it further.

For now, my bottom line is that PopSlate is a promising idea that is primarily for displaying images, as long as you’re okay with them not being in color. If that works for you, or you are comfortable using IFTTT, then PopSlate will be a useful addition to your iPhone 6.

If not, I suggest waiting to consider buying it once the automated third-party feeds are in place later this year.