Not as good as expected (or hoped)

I was looking for a high-quality adapter to let my Archos Gmini400 run through the car radio. After the positive reviews here I hoped a first class product, but was brought back when trying out on the floor of the facts.
First, the very loud running noise falls on with clickers in the drive bay. Cassettes run much quieter, why is that not even with such an adapter possible?
Then the volume was very low, unlike here described and hoped for from me. When experimenting noticed that when I pressed the adapter with a finger in the drive bay downward, the volume was much higher, approximately at the level of the tuner. The problem described in the products of other manufacturers due to the insufficient volume will therefore usually associated with the position of the adapter in the cassette tray. Obviously, the two tape heads need to be in a certain position to each other, so that the desired output level is achieved. Directly after the insertion is at any rate my radio not the case.
The sound quality has also not blew me away as a high-quality, well-recorded cassette still sounds better. During the journey that is certainly negligible in all the background noise, but clearly heard in the state.
Conclusion: If that's the best cassette adapter, how bad must then only the other brands be ?! If you value quality, imo should save a little money and then set an MP3-compatible car stereo (or just one with line input, if there is ...).