It's a pretty good bluetooth adaptor, as long as your device is within a few meters of the unit and in the same room. Sound quality is good, but breaks up if you go into another room. I also invested in separate Cable Mountain Phono RCA Cables which are a good addition for a few quid extra.
I should have listened to other reviews. Having bought this recently I can concur that it is not really designed as a rear light because the mounting/strap is does not allow for horizontal mounting anywhere on the rear of the bike - accept for under the seat. This really limits where you can put it and potentially ends up with you mounting it somewhere that's not ideal and potentially other road users might not be able to see it from all angles.
It's a shame - because the light itself is great. I may have to come up with a DIY solution to mount it better.