I have looked at several online tutorials for installing the device and accordingly tried to recreate what was difficult and I am technically talented.
In the end I still needed an ISO adapter for 36 euros, since not all lines found their way into the car radio. Still cheaper than the installation by a specialist, but with Rumgefahre to div. Time professionals rather expensive.
Defakto absolutely unprofitable without corresponding voucher!
Speakerphone quality OK