This thing has some serious shortfalls IMO. It sounds ok, my previous $30 one that I replaced sounds better with better staging at all frequencies.
My Zen Blue is running directly into my studio monitors so there's no amp and I cannot EQ the sound. The midrange is quite washed out, too much low end, highs are ok. Overall I can tell that this unit would sound great if you're using regular speakers in conjunction with an amp. The type of music makes a huge difference too — jazz and older recordings sound great, but anything modern / electronic / hip hop sounds a bit muddy.
It would really help if they released an EQ app update — even though reading on their site they're against it because it creates some kind of distortion.
And another huge minus for me: Even with the pairing voice turned off, the loud ding it makes when pairing is very annoying. It's completely unnecessary and so aggressively loud that I worry it will damage my speakers. Mine are always in standby mode or on because I'm listening to music all day so this becomes quite unpleasant.
Why do all the bluetooth companies have this loud sound? It's really grating.