One way to stand out in a crowdedcategory of devices is to employ a novel hardware design. Last year, Sony got decent marks from many reviewers, including me, for an Android tablet called the Tablet S, crafted to look like a magazine, with one thick, rounded vertical edge that made it more comfortable to hold than many other tablets. Now, the company has brought out another Android tablet with an even more radical design, and this one shows the limits of novelty.

The new Tablet P, sold in AT&T stores, is a 7-inch long, narrow, hingeddevice with no exposed display at all. When you open it, twin small screens are revealed. Content can appear on one of the two screens, or be spread across both. It can operate over either a Wi-Fi or a cellular-data connection.

It sounds cool, but the Tablet P has some crucial drawbacks. The most important one is that, to take advantage of its full viewing area by using both screens as a single display, you must put up with a thick, black, plastic bar across the center of whatever you're viewing. That disruptive scar is the inside of the hinge, where the dual screens meet.

Some apps avoid that absurd situation by cramming all their content into just one screen. But these screens are small, just 5.5 inches diagonally, closer to the area of a large smartphone than Sony's Tablet S or the iPad, whose screens are about 10 inches. When content is spread across both screens, as it is in the Web browser, the combined display is about 7 inches, but that black bar is present.

To be fair, Sony has modified or created some apps so they take intelligentadvantage of the dual screens, without the black bar to annoy you. For instance, the email app uses the bottom screen to list your messages and the top one to show whichever message you're reading. Similarly, the stock video player, and many games, use the bottom screen for control buttons and the top for the content.

But at launch, there are only about 40 such specially adapted apps out of the hundreds of thousands of Android apps the Tablet P can run. Sony says more will be coming, but I suspect that will depend on how many of these foldout tablets it can sell. And I can't recommend this one.

Sony has built-in on-screen buttons that can switch some apps from single-screen to combined-screen mode. But this isn't available in some common, crucial apps, like the Web browser and Google Maps, which must be run in combined-screen mode, with the bar in the middle. You can't run different apps in each screen, only separate parts of the same app.

Because it folds up, the Tablet P is much more portable than iPad-size tablets, or even 7-inch tablets like the Amazon Kindle Fire. It fits in a pants or jacket pocket or a modest-size purse. But when closed, its surfaces are rounded and have an overall thickness of a whopping 1.03 inches -- much thicker than a typical smartphone or tablet -- and so created a bulge.

There are other downsides. The Tablet P is relativelycostly for a small tablet. Sony sells it online for $550, more than the base iPad and much more than the $199, 7-inch Fire. AT&T sells it for $400, but that price requires a two-year contract costing either $35 or $50 a month, depending on how much data you want.

This new tablet comes with a paltry amount of memory. It is packaged with a 2 gigabyte removable memory card and 4 gigabytes of internal storage, of which just 1.8 gigabytes is available to the user. That is a total of less than 4GB, versus 16GB for the base iPad. You can buy a larger memory card, up to 32GB, but that adds about $30 in cost.

Battery life also is weak. In my standard battery test, where I play videos back to back with the screen at 75% brightness and both Wi-Fi and cellular connections turned on, the Tablet P lasted just 5 hours and 16 minutes, about half the battery life of an iPad. The battery is removable and a spare can be bought for $70.

And the cellular-data connection isn't the fastest type. While it is labeled as 4G, it doesn't use the best 4G technology, called LTE. In my tests, in the Washington, D.C., area, the Tablet P averaged just 3.7 megabits per second over cellular, versus more than 12 mbps for a new iPad running on AT&T's LTE network.

Finally, there is the hardware. I found the screens and cameras were OK, but the speaker was very weak. And, in the few days I was using it, a little door covering the USB port fell off and the top cover, which I had removed to insert a cellular SIM card, kept coming loose.

Portability is a virtue, and some companies are working on flexible screens that could bend without exposing a hinge. But in my view, the Tablet P doesn't cut it.