We've seen optional modules before, and they pretty much were a nonstarter. Here's how Moto modules actually work in the Moto Z.

Ask anyone who's ever played with magnets. There's something strangely satisfying when the two pieces come together. Almost like there was no stopping them. Some invisible force working its magic.

Nerdy? Yeah. But there's something about that effortless force, ya know? And it's been a bit of a crapshoot over the years when it comes to magnets and mobile devices. Either they work great, keeping everything where they should be, or you end up with a mess that takes too much force to unstick.

And that brings us to magnets and the Moto Z.

Moto Z, Moto Mods and LG G5

Actually, let's back up. The Moto Z is the second phone we've used this year that employs modular — in this case, Moto Mods — optional accessories that add some sort of functionality to the phone. And the Moto Z, at launch, has three — an extended battery, a speaker, and a pico projector. (There's actually a fourth — the Style Shell back that comes with every phone.) To switch modules, you just break the magnetic bond on the back of the phone, and pop the new back on. The Moto Mods have chips in them that talk to a co-processor on the phone, and the two sync up seamlessly.

The Moto Z isn't the first to try optional accessories, but it's the first to make them work.

LG tried its hand at this sort of thing earlier in the year with the LG G5. It was a very different experience. I (and other journalists) got an early look at the LG G5 ahead of its unveiling at Mobile World Congress, in late February in Barcelona. Figuring out how to remove the modular section in the G5 was simple enough. There was a button to start the ejection process, the butt would slide out a few millimeters, and the connected battery would come with it. But I remember standing there the first time, clueless as to how the battery could come off the butt. (Hint: With a decent amount of force.)

It wasn't overly intuitive, it wasn't without effort — and you had to reboot the phone to get it to work. And complicating matters for those of us in the United States was that the the more compelling of the two modules — a high-definition digital-to-analog audio converter — was never made available.

The Moto Z? You remove the back with a fingernail. The Moto Mods have a convenient little slot for getting things started. Then you just pop on a new one. And by the time you flip the phone back around to get to work, the software has done its thing, and it's ready to go. That's not to say that the Moto Z will enjoy success with its modules that LG didn't. That's all but certain. It's just that Moto has implemented them infinitely better than LG did.

Two phones. Two sets of optional accessories that add functionality to the host device.

And only one that you can use without any explanation whatsoever.