In 2013, a Dutch designer named Dave Hakkens posted a YouTube video called Phonebloks. It went viral (about 22 million views), because its logic was so compelling: We should be able to snap together the various components we want in a smartphone: camera, processor, storage, GPS, screen.

We’d save money, we’d replace only individual components as technology improved, and we’d stop pouring 2.5 million tons of sharp, toxic, non-biodegradeable electronics into our landfills every year.

Compelling, yes; practical, no. For example, a modular phone would be much bigger and bulkier and uglier than today’s integrated, unified models. And that’s assuming you could persuade the Apples and Samsungs to embrace the modular concept; they love that we throw away our phones every year. (Google experimented with a modular phone project, but eventually shut it down.)

All of which brings us to the Moto Z family.

Three things make these 5.5-inch Android smartphones radical, innovative, and risky.

First, they’re thin—the thinnest in the world, Moto says. The Moto Z model ($700, available for any carrier) is only one-fifth of an inch thick; you could practically fold it like a paper airplane. Its sibling, the Moto Z Force (Verizon [VZ] only), costs $20 more and gets you a higher-resolution camera and longer battery life—yet it’s still thinner than a Samsung Galaxy S7.

Second, the Z and Z Force have no headphone jacks. So you’ll have to carry around the included adapter to accommodate normal earbuds, just as on the iPhone 7.

(The new Moto Z Play is fractionally thicker, has a lower-res screen and slower processor, and lacks the shatter-resistant screen and optical camera stabilizer of the others. But it restores the headphone jack, its battery goes for days—three or four between charges—and it costs only $408 from Verizon, or $450 from Moto for use on other networks.)

But third—and this is the big news—the Moto Z phones are, in fact, modular. Now, don’t get excited; they’re not nearly as modular as the Phonebloks or Google’s Ara concepts. Instead, each phone can accommodate one new component that magnetically snaps onto the entire back.

At the moment, there are five of these Modo Mods available: interchangeable back panels, stereo speakers, battery pack, projector, or camera. Here’s a rundown:

* Style Shells ($20). These are thin, light back panels made of cool materials like wood or nylon. You can use the phone without one, but it really looks as though it’s expecting something to snap on; the Style Shell completes the phone by adding a smooth, slightly rounded back.

* JBL SoundBoost Speaker ($80). When you snap this speaker onto the phone, the sound of your music or movie instantly starts coming out of the JBL speakers. No settings, no switching, not even a power button. The sound is like what you’d expect of, for example, a Bluetooth speaker about this size: Big and much richer than what a phone can provide by itself. The built-in battery goes for 10 hours on a charge, which is a pretty long party. A built-in kickstand props the phone up for video watching—and turns the table into a resonant surface for the downward-firing speakers.

* Incipio OffGrid Power Pack ($60 and up). Backup battery packs are nothing new. What makes this one cool is that it also adds a feature to your Moto: The ability to charge just by setting it down on a charging pad.

* Moto Insta-Share Projector ($300). Yes, you read that right: projector. This Moto back panel is actually a medium-powerful LED pico projector. Snap it on, press the On button, pop the kickstand out, and everything you see on the phone’s screen is now blasted onto a wall or ceiling. As with most pico projectors, the image isn’t very bright unless the room is dark (50 lumens); if the room is dark, a picture as big as 70 inches is watchable. (The auto-keystone correction is amazing; no matter how you tip the thing, the projected image snaps to perfectly rectangular.) The battery lasts for only an hour, though, and the resolution is only 854×480—not, in other words, high definition. You have to charge the projector separately.

* Hasselblad True Zoom ($200 ). This add-on gives your phone a 10X optical zooming camera.

The Mods are amazingly designed. You snap them on and do nothing—there’s no pairing, no OK button, no software switches. They just work, instantly and reliably. Life, at this point, has taught us that there are always steps to connect one gadget to another, so it catches you by surprise every time these things just work.

They’re not, on the other hand, a very good value. You’d have to be a serious Moto nut to buy that $300 projector, with its one hour of battery life and crude resolution; it’s easy to find brighter, longer-lasting hi-def pico projectors for that price that work with any phone. The speaker is cool, but $80 would also buy you a very nice Bluetooth speaker that sounds better. The Hasselblad camera takes mediocre photos and its software is half-baked, according to CNET’s review. And the wireless-charging battery pack—well, OK, but don’t forget you still have to buy the charging stand.

That problem gets worse when you remember that they work only with this phone. When it comes time to upgrade to a new phone in two years, all of your Mods may well be worthless junk.

But what about the phone?

The mods may be middling. But the phone is fantastic.

If a phone from Apple (AAPL) and Samsung packed this much clever engineering and innovation, we’d be swooning in our seats. (Why isn’t there such a thing as a Moto fanboy?)

This thing is packed with Moto’s traditional clever gestures and smart features. Some of these require turning on in Settings, but take a look:

• You can wave your hand over the sleeping screen to wake it and read about any missed notifications.

• Jump straight into camera mode by twisting the sleeping phone twice (or double-tapping the Home button).

• “Chop” twice with the phone, karate style, to turn the flashlight on or off (the back-panel LED). Glorious.

• Put the phone face down to turn on Do Not Disturb mode.

• Stop the phone’s ringing by picking it up. Just as your parents did for decades.

• When you want to speak to the Android voice assistant, you don’t have to say “OK Google.” You can choose any introductory phrase you want.

• The phone won’t go to sleep while you’re looking at it. How great is that?

• You can set things up so that your password isn’t required in situations where it’s pretty clear that it’s you using it: when the phone is connected to your car or smartwatch, when the GPS tells the phone that you’re at home, or even—get this—when the phone detects that it’s on you, in your pocket. (It locks only when you set it down somewhere.)

• You can also unlock the phone either by voice or by face. (That is, the phone unlocks when it recognizes you.)

• The phone can announce incoming calls and text messages while you’re driving or using a headset—hands free. That’s brilliant. (You can even specify a geographical location for this feature to kick in, so it’s not happening all the time.)

• All three Moto Z phones come with Turbo Chargers, which means they recharge really fast. After charging the phone for only 15 minutes, you can get 8 or 15 hours’ worth of charge (on the Moto Z and Z Force, respectively). Now, that’s a feature that means something.

• The Moto Z’s charging jack (and headphone jack) is the sensational USB-C, which you can read about here.

• You can expand the storage with a microSD card. (Nobody would dare build an expandable phone without a card slot, would they?)

And don’t forget: this phone is thin.

Really, you might wind up with only three complaints.

First, the fingerprint reader doesn’t double as the Home button, as on Apple and Samsung phones. You’ll spend your first week trying to click it by mistake. (On the other hand, you can touch the reader to unlock the phone, and touch it again to put the phone to sleep. Nice.)

Second, without something attached to the back, the phone is insanely thin but feels incomplete. There’s a metal ridge outline that screams, “Attach something here!” And the camera cylinder pokes out absurdly.

Third, the Moto Z’s camera is fine, but not up there with the Samsung and Apple cameras. It occasionally gave me some weird white-balance problems (color casts).

So, here’s the sad thing: The Mods feature probably won’t catch on. Despite the genius of the concept and the execution, they’re just too expensive, thick, heavy, and limited. You could buy each thing—battery, speakers, projector, camera—as standalone units that won’t be worthless when you get a different phone someday. For much less money, and with much better features, .

But the actual phones are terrific—some sensational pieces of engineering. Thank you, Moto, for showing that there’s still room for radical innovation in the smartphone design. May Z Force be with you.

David Pogue, tech columnist for Yahoo Finance, welcomes non-toxic comments in the Comments below. On the Web, he’s davidpogue.com. On Twitter, he’s @pogue. On email, he’s [email protected]. Here’s how to get his columns by email.