Unfortunately, the tradeoff of the BlackBerry Mini Stereo Speaker's tiny stature is that it lacks the audio muscle of bigger wireless speakers. With small drivers and a minuscule chassis, the Mini Stereo doesn't have the space to develop much richness or depth of sound. As a result, music played through the device was tinny, muddy, and flat. Volume did get fairly loud, but there was no bass to speak of, a shortcoming I especially noticed listening to dance, electronic, and rap tracks.
By comparison, audio piped through the JBL Flip had much more oomph in terms of bass, stereo separation, and volume. High, mid-, and low frequencies were more balanced, too, when stacked up against the BlackBerry Mini's brash, lifeless frequency response. To be fair, though, the Flip's footprint is about three times the BlackBerry Mini Stereo Speaker's.
Using the BlackBerry Mini Stereo Speaker to make calls gave mixed results. On my end, voices sounded surprisingly rich and warm. People I was speaking with, however, described my voice as thin and muffled. They also complained that I sounded distant, particularly when I used the device clipped to a chest-level bag strap.
One bright spot in the speaker's performance, though, is its long battery life. BlackBerry claims the device will provide up to 16 hours of talk time and can stream music for as long as 14 hours on a single charge. In my experience, after an initial charge the speaker persevered through my entire weeklong test period, which consisted of light use (a few hours a day), without needing a recharge.
I won't deny that the BlackBerry Mini Stereo Speaker is ultracompact and has an interesting design that sets it apart from other wireless speakers. Still, the primary task of any audio system is to produce sound that's pleasing to the ears. Unfortunately, this accessory falls short in this crucial regard. Sure, its battery has admirable longevity, but for $100 there are other, much better-sounding options.
I also have doubts about the practical appeal of the BlackBerry Mini Stereo Speaker. I'm not sure who would want to blast tunes or make calls via a bag strap, or even where or when you would do this. The best possible use that springs to mind is for a cyclist looking for a way to listen to music and make calls without relying on headphones. If you plan to use your portable speaker for entertaining a group, then I suggest opting for either the aforementioned JBL Flip ($99) or Logitech's UE Mobile Boombox ($99.99). Both of these produce fuller, more booming sound for the same price.