Every Android phone maker has a different approach to software. Some, like Samsung, go all out with a highly customized interface that touches every corner of the way Android looks and works. Others, like Motorola, stay true to the visual style of "vanilla" Android. Then, somewhere in between, you've got companies like Sony.

In recent years, Sony has gradually cut back on visual cruft, to the point where its current crop of phones, the Xperia Z5 series, look and behave a lot like Google's vision of Android. So what's next? Well, alongside its official firmware updates for Xperia phones, the firm last year opened up a "Concept" software program for fans. The big idea is to rework Sony's software from the ground up, using vanilla Android as a base and layering on Sony features as needed. Following the success of the original Lollipop Concept over the summer, Sony rounded out the year by bringing Marshmallow Concept software to a select group of Xperia Z3 and Z3 Compact owners. Verizon is offering the Pixel 4a for just $10/mo on new Unlimited lines It's a step closer to Motorola's way of doing things. But the Concept firmware is about more than just vanilla Android. The program involves Xperia owners in Sony's software development, using surveys and a Google+ community for further feedback and bug tracking. Effectively, it's a fast-moving yet surprisingly stable software track for power users. And it's pretty slick.

A fast-moving yet surprisingly-stable software track for power users Sony's Concept firmware runs on the Xperia Z3 and Z3 Compact, which are a couple of generations removed from Sony's latest stuff. Then again, they're based on the still-great Snapdragon 801, arguably a more stable development platform than the newer 810. It's a common misconception that it's UI stuff that slows Android phones down, and if only manufacturers would leave the OS as Google intended, all would be well. But stock Android doesn't guarantee speedy performance, as anyone who's used a Moto X Play will know. Code still needs to be optimized, and stutters smoothed out, and that's exactly what Sony has achieved with its Concept firmware. (Of course it also helps that they're starting from scratch with minimal bloat.) The result? Probably the fastest Android phone I've used, and that includes 2015 models like the Nexus 6P and Samsung Galaxy S6 edge+. This software absolutely flies, putting to shame the vast majority of newer and more expensive handsets. The Xperia Z3 on the Marshmallow Concept firmware is probably the fastest Android phone I've used. The Marshmallow Concept's performance is about more than app load times and animation fluidity, though. The Z3's battery life — already pretty good even back on KitKat — gets a welcome boost thanks to Android 6.0's "Doze" feature. You'll miss out (for now, at least) on Sony's Stamina mode, which lets you cut down on background activity to save juice. However Marshmallow's built-in power-saving features mostly make up for this. Much of the Concept firmware looks and feels like vanilla Android. The phone dialer and contacts app are faithful recreations of Google's stuff. And the same goes for core UI stuff like on-screen keys, the lock screen and the notification shade. There's been some icon swappage in the Settings app, but the way this works is largely unchanged.