In short, impossible to any music stored on USB key, I do not even speak bluetooth ...
One day, a friend showed me a pass delusional thing: he passed his music from his phone in his car ... "Ouhhaaaa !! great, how you do that ??" ... He had installed Parrot car kit - Kit bluetooth car - CK3100. Good, but 100 still, besides that we must also dismantle the dashboard.
So, I chose this small FM transmitter, a little worried I confess. Well actually, that's fine. You plug into the cigarette lighter, you choose the FM frequency you set your position on said frequency, and its progress. You can play from a USB drive, a connected audio device with jack cable (supplied), or device through Bluetooth. A remote control is provided (untested)
The sound is good, but I have some parasites bluetooth I do not hear from the same source equipment connected by cable jack. Maybe it's the source, I have no other to test.
This unit can also be used as handsfree phone, although in my case, I was not able to use it properly. The sound passes well on the speakers, but the phone's microphone off seems (apparently a microphone is available on the steering remote control of the unit and must take over the phone, but as I do not use the remote control ...)
One regret: no use RDS to display the name of the songs on the radio display.