The smartphone has been called the "PC in your pocket". Can it really serve that purpose, though? Can it really be the one device to rule them all?

Microsoft has a new feature called Continuum that, once again, attempts to do just that — create one converged device to meet all your computing needs. In a world of declining PC sales, is Continuum something Apple should consider as well?

The idea of a single device that works as a phone and a PC has been tried before. In 2011, Motorola launched the Atrix. It was an Android phone that could connect to a laptop dock and become a "PC". While the phone was okay for the time, the practicality of the device was greatly limited. Bottom line, it just didn't work.

The same year, Asus launched the Transformer. It was an Android tablet that could convert into a laptop by docking into a keyboard. A year later, Asus introduced the PadFone, an Android phone that could dock to a tablet and then connect to a keyboard. All of these felt like concept cars — interesting ideas that were never meant to come to market. Except these particular concept cars actually came to market.

Here's how Continuum works: Take a Lumia 950 or the 950xl, connect it to a display dock with USB and HDMI outputs, add a Bluetooth or USB keyboard, and it delivers what Microsoft calls a "desktop PC-like" experience. To get a better sense of it, I spent the last two days trying to be productive with a Lumia 950xl, a 60" HDTV, Bluetooth keyboard, and mouse.

While Microsoft uses "desktop PC like" to describe the experience, it isn't quite that. It looks like Windows proper but in many ways feels like Windows CE all over again. (That's what powered those first Pocket PC devices that worked so hard to look and feel like Windows but never really worked like it.)

Continuum only works with new Windows 10 Universal applications. At the moment, those are few and far between. The most is Microsoft's own Office. Continuum's desktop experience looks superficially like Windows (uppercase) but doesn't actually do windows (lowercase). Applications must be switched through Alt-Tab. Continuum does support BT keyboard and mice, as well as USB devices. It's interesting in theory, the idea of connecting to multiple monitors and peripherals in multiple locations. In practice, though, it all fell apart for me.

The idea of carrying a display dock, an HDMI cable, as well as external mouse and keyboard, felt like more work than simply carrying an extra device optimized for form and function. For example, an iPhone and an iPad.

So why Continuum? In a post-PC world, where Windows is no longer the cash cow it once was, Microsoft is attempting to differentiate themselves from other platforms by offering a novel experience. It's a seductive idea, and some companies like HP and Citrix are trying to improve on with more integrated devices and virtualized environments for Enterprise but, in my opinion, it's just not here yet and may not be any time soon.

For people totally committed to the Microsoft ecosystem, Continuum will have some appeal. Where it will struggle is in going beyond that and gaining real momentum.

Where the phone experience if fine, Continuum itself is still frustrating and doesn't deliver the experience Microsoft promises. It takes a small step in the direction of a single device, but given the small share of Windows phone — and the number of phones that can use Continuum — it's hard to see how it can become more than a novelty.

There seems to be an idea that this concept would be useful in emerging markets. Unfortunately, with all the accessories needed to make the experience work, as well as the high cost of devices that it currently needs, it would be far more effective for most people to own a smartphone and a full personal computer. This logic feels to me much like the One Laptop per Child project — which went nowhere.

Ultimately, it's a hard recommendation for either businesses or consumers. Like touchscreen on Macs, it's a direction I don't see Apple moving towards.