In terms of convenience (decent tone at low volume, transportability) this amp is a life-saver. In terms of sound, however, it is not very good. In terms of its features (EQ, overdrive, delay, headphones/EM out), it is okay.
I use this as a practice amp in an apartment building with thin walls & ceilings, and for that purpose it is great. At low volumes, I can get a decent and consistent enough tone to be able to experiment with my pedalboard. It is small enough to travel with easily, which is great as I occasionally spend time abroad.
However, the tone gets muddy and inconsistent at higher volumes, especially in the bass frequencies. And don't expect high volumes from these speakers either, they are certainly not loud enough for any live situation. Though you can probably use the EM output to run it into a mixer or PA, I would not recommend purchasing this amp for that purpose.
The single mid scoop EQ knob will allow you to dial in some different, though limited, tones, and there is also an overdrive switch which I don't much care for, as I have pedals for that (though again, at higher volumes neither will sound very good). The built in delay is a nice feature, as you can control both delay time and intensity, though honestly I would have preferred reverb.
You CAN use these as computer, smartphone etc. speakers as advertised, but they do not sound very good, nor very loud. All dedicated computer speakers I have owned in a similar price range sound vastly better (and louder) than these Blackstars. Also, the volume control on the amp will obviously not affect mp3 input, which, again, makes them inconvenient as computer speakers.
All in all, I somewhat regret not having saved up a bit more money to buy a Roland Micro Cube Bass amp or something similar, which you can also use live. On the other hand, I'm spending 5 months abroad next year, most likely in a student dorm, and this is probably the best sounding amp I could easily and reliably bring with me, so it really depends on your needs!