I’ve been spending a fair bit of time with Windows convertible tablets lately. I reviewed the Samsung ATIV Smart PC Pro 700T last week, and I’ve had the Asus VivoTab RT kicking around in my benchmarking lair for a few weeks. I’m also currently testing an Atom-based tablet: the VivoTab Smart, which combines x86 support with the slender profile and long battery life you’d expect from an ARM-based device.

Oh, and I’ve tried both versions of Microsoft’s Surface. Not in my office, though—there was a Microsoft kiosk at the mall, and I stopped by while shopping for a Valentine’s Day gift. Yes, I’m that romantic.

Anyhow, the longer I spend with these devices, the more I grow convinced that convergence à la Microsoft is an ill-tasting recipe. I articulated some of my reservations in the Samsung 700T review, where I stated:

There seems to be little overlap between what people do on tablets, which is mainly content consumption, and what people need full-featured notebook PCs for, which is productivity. . . . So, why must we have both on one machine? What’s so compelling about having Facebook and Kindle apps on the same physical system as Office and Photoshop? Since the combination is fraught with compromise, why not get a great tablet and a great ultrabook rather than a less-than-great combination of the two?

TR’s own Geoff Gasior had a reasonable answer to this: because carrying one device is better than carrying two. And hey, I totally get that. My problem is that saving room in my backpack does me little good if I it means passing up the best tool for the job. From my experience so far, Windows convertible tablets are rarely—if ever—the best tools for the job.

Think about it. What do you want from a tablet? You want plenty of quality apps to choose from, including games. You want a great display, long battery life, and something that’s thin and light. You also want a device that’s both fast and easy to use, because content consumption is no fun if waiting and troubleshooting are involved.

Win8 and WinRT systems just don’t deliver there. Good Modern UI games and apps are still pitifully few in number. (There’s no Flipboard, Feedly, or Google Currents. No HBO GO or BBC iPlayer. No Yelp, and no official Facebook client.) The handful of Windows tablets that are thin, light, and endowed with long battery life—those with Atom and ARM-based processors—all seem to have ugly, low-resolution displays. (1366×768 is just downright sinful on a tablet screen.) As for speed and ease of use, WinRT slates take forever to launch apps, and while Atom tablets strike a passable balance between performance and power efficiency, ease of use remains a concern. One must still put up with the awkward marriage between Modern UI and the desktop, not to mention the questionable design choices within the Modern UI environment itself.

Okay, now what do you want from a good laptop? This is a system you’re going to be using for productivity, so you want it to be fast. You want a great keyboard and touchpad, because controlling Windows 8’s desktop environment with a touch screen is an exercise in frustration. If this is a productivity machine, chances are you want more than 11.6 inches of screen space. Don’t get me wrong; small, highly portable notebooks are great. Photo editing on a thimble-sized display, however, is not. Neither are the cramped keyboards and truncated touchpads that invariably accompany smaller screens.

Windows convertibles also fail to deliver in this department. For them to double as half-way decent tablets, convertibles must sacrifice desktop performance and capabilities in one way or another—either with plodding performance, like the Atom-based systems, or with a “let’s pretend” desktop courtesy of Windows RT. They must restrict themselves to 11.6″ or smaller screen sizes, as well, which inherently compromises the keyboard and touchpad arrangement. Worse, that compromise is often more dire than it ought to be. The Surface’s Touch Cover is just plain awful (try touch-typing on the thing, I dare you), and the Samsung 700T’s fickle and undependable touchpad really disappointed me.

Ideally, Windows convertible tablets should offer the best of laptops and tablets, all in a single device. They should, but they do not. Current offerings feel more like crappy tablets rolled into crappier notebooks—jacks of all trades, masters of none, with good design sense and usability discarded in the name of convergence.

What does that convergence get you?

Well, you can store all your music, photos, and personal files on a single device. That’s nice, I suppose. Then again, cloud storage is starting to make that convenience a little old-fashioned. I don’t carry very much music on my phone, for example, because I don’t have to. When I want to listen to something that’s absent from the device, I simply grab it through iCloud over the LTE connection. (And no, being an Apple-worshipping metrosexual isn’t a prerequisite. Google and Amazon run similar services.)

What else? We’ve already addressed the saving-space-in-your-backpack thing, and I think the downsides of convergence make that a lopsided bargain. That leaves one major advantage: cost. Buying a convertible tablet is cheaper than springing for a separate tablet and notebook, isn’t it? If you’re strapped for cash, convergence must be a pretty solid proposition.

The price difference isn’t as big as you’d expect, however. A Nexus 10 will set you back $400; an iPad, $500. An entry-level ultrabook can be had for $650, and a good one will cost about $1,000. Now look at Samsung’s ATIV Smart PC Pro 700T—a fine example of a Windows 8 convertible with ultrabook-class performance, which is precisely what you need if you aren’t buying a separate laptop. It costs almost $1,200 at Newegg. That’s $150 more than the Nexus 10 and the inexpensive ultrabook, and only $300 cheaper than the iPad and deluxe ultrabook combo.

Now, why on Earth would you settle for the worst of both worlds?

Don’t get me wrong; convergence can be done well. Smartphones are touch-based computers converged with mobile phones, and they’re are a great example of the concept taken to the right place. In that instance, though, convergence works because people don’t want their pockets weighed down with extra hardware. In your trouser pockets, every ounce and every cubic inch counts. That’s why nobody seems to mind that smartphones have pitiful battery life compared to basic cell phones. The benefits of convergence—having a little, Internet-connected computer, media player, and gaming console in your pocket—far outweigh the inconvenience of having to charge up every night.

I don’t think you can make a strong case for convergence between tablets and notebooks. You don’t carry those devices in your pocket. You carry them in a backpack, a briefcase, or a messenger bag, and so it doesn’t really matter whether you’re hefting a tablet and an ultrabook or a tablet and a removable keyboard dock. There’s a small weight and thickness difference, but it doesn’t amount to very much. The Samsung 700T weighs 3.54 lbs when docked. Put together, the iPad and deluxe ultrabook we talked about weigh 4.3 lbs. We’re talking about a 12-ounce disparity, which is nothing compared to the nuisance of having to carry both a phone and a PDA in your pockets.

Of course, none of this means successful notebook-tablet convergence is unachievable. Once the hardware delivers ultrabook-class performance in the power envelope of a Tegra 3, and once Modern UI is sufficiently polished, fine-tuned, and loaded with great third-party apps, then I expect we’ll see some excellent convertibles—devices good enough to make me ditch my iPad and my laptop. Perhaps all it will take is the next generation of processors—Haswell, Bay Trail, and Temash. Or maybe only Windows 9 and next year’s hardware innovations will bring us there.

Or maybe it will take even longer than that.

For now, though, I’ll keep watching Windows convertibles as I always have: with a mixture of curiosity and disappointment.