The most impressive thing about the REX portable speaker from Boombotix is how much volume pumps out of the tiny thing. It's small enough to attach to your belt (and has a clip for doing just that), but you can really pump up the volume with surprisingly little distortion (notice that I didn't say there was no distortion — because there is when you push the volume a bit too high).
I was testing out the REX in our living room at home, playing tunes from my iPhone 6s Plus via the seamless Bluetooth connection. Both my wife and daughter came into the room, asked me to TURN THAT MUSIC DOWN, paused, then asked, "That's coming from that little speaker?" I suspect that's a common reaction most REX owners will get.
The sound quality itself is good, but not great. The bass a is a tad weak, and the mids a bit underwhelming. That said, the overall audio quality is as good as I've heard in any speaker this small.
The $59.99 speaker comes in a variety of colors. You can buy custom grill kits (think "skins") for your speaker. Behind the grill is a pair of 3-watt drivers in a side-by-side array, as well as an LED that glows different colors depending on the charging or pairing status.
The REX also has a built-in speakerphone, a rechargeable lithium ion battery (that offers up to six hours of battery life after a one-hour charge), andlines in/out to hardwire it to a Mac, MP player or other device. With its polycarbonate parts, IPX5 waterproof rating (it can handle splashes of water, but don't let it get submerged), and small size (3.2 by 3.4 by 2.2 ) it's ready to go just about anywhere.
In fact, if you want an ultraportable, extremely durable, and good-sounding speaker system, there's no better all-around choice (at least that I've found) than the Boombotix REX.