Good sound for its size
I'm not going to lie to you and say this sounds great. But like I said with the previous model, when you get into the tiny-speaker category, just sounding OK is a feat, and most people should be impressed that such a small speaker can produce fairly decent sound. It can play pretty loudly and puts out a lot more sound than the internal speakers of your typical smartphone or tablet.
The Mini Boom offers slightly better bass performance than its predecessor. As I said in the intro, it's not a huge difference, but the speaker does sound a little better overall, with slightly cleaner, richer sound (to be clear, this is a relative statement). Still, even with the improved bass response, you're not going to mistake this for a big speaker. It does sound a little thin and not terribly open or expansive. But for a small speaker it manages to output a good amount of sound with bass that has a little warmth to it. (I'm sorry I don't sound more enthusiastic, but I've listened to a lot of these tiny Bluetooth speakers and they all have their limitations).
Combining two speakers didn't produce sound that was twice as good, even though you get better stereo separation in "stereo" mode. The fact is adding a second speaker doesn't improve the bass (you're still left with the same sound, it's just magnified). In other words, I wouldn't bother doubling up, and would instead buy the better- -- and bigger- -- sounding UE Boom, which retails for $199.99.
As far as battery life goes, you can run this for about 10 hours before having to recharging it, which is pretty decent. I found that it worked well enough as a speakerphone, though you'll want to keep it within a few feet of you when talking into the integrated microphone.
Some readers had asked me to review the updated version of UE Mobile Boombox after it got its name change to the UE Mini Boom and was updated. One reader had heard, "It was much better."
It isn't. It's just a little better.
And in the meantime, the competition has increased. You have speakers like the OontZ retailing for $50. It may not play quite as loud, but it also delivers decent sound for its size and costs less. The UE Mini Boom is a better built speaker. However, I can't say it truly stands out from the pack at this price point (you also have the JBL Flip at $99).
That said, it remains a solid mini Bluetooth speaker and is a pretty safe choice, especially if you can get it for closer to $80 instead of $100.