I thought the Solo -- a mono speaker -- sounded relatively good. Yeah, it's a little tinny (all these small speakers are), but it output a lot of sound for its small size and had some bass (the speaker incorporates something called X-Bass technology, whatever that is).
If that doesn't sound like a ringing endorsement, it isn't. It's hard to get too excited about the sound of any of these tiny speakers. Most of them, including the Solo, distort at higher volumes, and they just don't handle bass-heavy or complicated music well (I found myself cringing at times). In other words, you can stick a logo on the speaker that says X-Bass, but if you run hip-hop through this guy, it's still going to sound comparatively thin and hollow to a bigger speaker that has some kick to it. However, with other tracks, particularly simple acoustical ballads, I found myself saying, "OK, that sounds pretty good."
All that said, I'll give the Solo credit -- it held its own against the competition. I thought the $50 Oontz sounded a little better. But the Solo is smaller, easier to carry around, and has an eye-catching design. In terms of sound, it's right there with the Philips SoundShooter Wireless but has that extra audio output and seems a little more durable.
The $50 HMDX Jam Plus is a little bigger, and it also fires straight up. The Jam Plus' advantage is that you can pair two units together and turn them into a set of left/right stereo speakers. The Divoom Solo has the advantage of being smaller and having the speakerphone capabilities. It would be hard to pick between the two, but if portability is a priority, the nod would go to the Solo.
I tend to encourage people to step up to more-expensive compact Bluetooth speakers such the $99 JBL Flip or even the $199.99 UE Boom or $199.99 Bose SoundLink Mini. Of course, a lot of folks are on a tight budget and want to stick to something under $50.
If you fall into that category and are looking for a tiny Bluetooth speaker, the Divoom Bluetune Solo, despite having its performance limitations, sounds relatively decent (compared with other tiny $50 Bluetooth speakers at least) and has an attractive design and good feature set. It tends to sell for $49.95, but I've seen it at some online retailers for $39.99, which is what I think it should cost. At that price (and even at $49.95) it's certainly worth considering if this is the type of very portable wireless speaker you're looking for.