Ok with a few caveats

Since my car stereo unfortunately does not support MP3 and etc. Also no connection for USB available, I came to use an FM transmitter to the idea. The CD stack in the car with the times a bit nervous.
After some research, and because of the good reviews I decided to MusicFly Select.

The device makes a stable impression and the service is both on the unit and remote control super easy.
Since the connection disappears quite deep in cigarette lighter, I had to plug it with me to the side at all to be able to connect a USB stick the device.
The Soundqaulität is mediocre to ok. I tried it with both the automatic and the manual frequency search. Unfortunately, there continues to be a quite strong noise, which is extremely annoying especially during quiet passages of music. However, one must say that the volume needs to be a bit higher then. In quieter background music there is actually no problem.
Nevertheless, the quality of normal radio stations is a lot better.

Somewhat unfortunate is the Administrative Tools folder. The device supports up to 20 folder. The order, however, depending on the order in which it stores the folder on the USB stick. Why you can not just number the folder is a mystery to me. For each track numbering works.

The display of the ID tags via RDS radio display works with limitations.
For example, if Albums Cover are stored in the tag, the display stays blank.
Also scrolling in the radio display is not particularly liquid and always remains fairly long.

All in all, the device is in order. Etc. for rock music recommended, definitely for classical or soft music generally not.
For the high price I had expected a little more.
Will probably still think times for a new radio.