How does the Mini sound? Well, while it just can't deliver the performance of a larger speaker, for what it is -- and its tiny size -- it sounds very good.
The one thing I noticed about it more than some other speakers is that placement makes a big difference. Putting it closer to a wall definitely improves bass response and the speaker sounds fuller. It also plays pretty loud -- louder than the Jawbone Jambox, for instance -- but it's clear that Bose's engineers had to restrain the sound a little in order to avoid distortion at higher volumes. You can kind of feel the speaker wanting to go louder but those finely tuned algorithms running through Bose's digital signal processor (DSP) are keeping it from going too far and doing something it shouldn't.
Overall, the sound signature is somewhat laid-back and forgiving; sound is a bit creamier. The bass goes pretty deep, but it doesn't sound incredibly tight or punchy. All in all, however, you come away with the sense that Bose eked out about as much as it could from a speaker this size. It can fill a small room with sound and does all right in medium-size rooms, too.
As for battery life, Bose says you'll get 7 hours of play time and a 3-hour recharge time. I managed to use the speaker over the course of an 8-hour workday without a problem, though I was listening at moderate volume levels and I did take a short listening break for a 30-minute lunch. That's fairly decent, though some speakers are rated at over 10 hours of battery life.
Comparing the Mini with such products as the similarly priced Beats Pill, the Bose comes out the winner, with better sound and slicker design, though the Beats Pill does include a carrying case and have speakerphone capabilities. I thought the $100 JBL FLip had a little bit brighter, more forward (aggressive) sound, and played about as loud, but the Bose's bass was bigger and could go deeper. And the $200, the UE Boom has slightly bigger sound, better battery life, and a built-in speakerphone, as well as being water-resistant and better suited for outdoor use.
As an editor at CNET, I get to try a lot of Bluetooth speakers out. A new one seems to show up every week and many of the small ones tend to sound pretty similar. By that I mean the average consumer would think they sound pretty good for their small size, but they tend to sound a little thin and distort sound at higher volumes, particularly with bass-heavy material. I'm less critical of affordable models ($60 or less) but tend to be tougher on small speakers that cost over $100 and fail to deliver high marks for design and performance (features counts a little less).
In terms of price, of course, the Bose SoundLink Mini is at the high end of the spectrum for ultracompact Bluetooth speakers. That said, it's a step up in design and build quality from most of the competition and while it has its sound limitations (a tiny wireless speaker can only sound so good), it delivers bigger, fuller sound than most similarly sized Bluetooth speakers. In other words, it definitely stands out from the pack, even if in some cases the sound difference is relatively small -- JBL's Flip and Charge, for example, deliver very good sound for the money. I also wish the Mini had an integrated speakerphone and came with a protective cover, though the inclusion of a charging dock helps mitigate those omissions.
For me personally, I'd have a hard time choosing between this $200 model and the $200 UE Boom, which I think is a bit more versatile and better suited for outdoor use. Ultimately, it may come down to simple aesthetics and how you intend to use the speaker. The SoundLink Mini is targeted at someone who's looking for a very sleek wireless speaker that sounds very good for its tiny size and can be easily moved from room to room (and the patio) but at the end of the day will probably end up docked in a bedroom or home office, perhaps parked next to an iMac or MacBook Air. They do go well together.