I bought one of these via ebay about 6 months ago (for about £10 delivered from China). I agree the sound quality is not good enough when reading from the usb port, but it is fine if you connect your MP3 player with the headphone jack provided. I initially also had problems with the 5 or so preset stations as they often clash with various Radio 2's. I found however that this is also easily solved by just rotating the transmitter in the car power socket. When it comes down to it, it is not a perfect sound quality, but what do you expect when you are converting the sound to FM and back again, however if you use the headphone Jack it is certainly good enough if you are not an audio purist.
I had one too, the sound quality was poor.. no matter which channel i used it always sounded as if there was no treble, very dull and flat sound.
I had one of these from SVP, it was terrible, fuse kept blowing, very few channels to try and find that is not been used by broadcast stations.
It's cheaper at SVP :) https://www.hotukdeals.com/forums/showthread.php?t=42866