The sound is in my view no loss, as far as I could tell while driving. I therefore both own mp3 music played and the Spotify stream. The volume is a little weak, and I could not determine whether this is due to the settings of the smartphone or the adapter. But you can easily easily turn on the car radio. Course Switched TP adjusts itself automatically with me down a bit, I have set on the equalizer of car radios.
The adapter loads, as far as I have observed that, even during operation. A battery indicator that provides information about the charge state, is unfortunately missing, so I can not say exactly how accurate the use affects the consumption of energy.
