We recently acquired an A4 B8 for my wife. We bought it from a friend and while it was in generally very good condition the one annoyance was that it didn't have bluetooth audio. We could have added a bluetooth dongle to the AMI port but after a fair bit of research decided to order a Carplay/Android Auto interface.

We bought this one which was $270USD including DHL shipping. The seller was very responsive on chat and confirmed we'd selected the right unit.

It arrived here in Dubai in three days and I fitted it in about 2-3 hours. It came with a full loom kit so there was no cutting wires or soldering. It works with all the factory controls and the steering wheel controls work perfectly. It even came with a factory Audi microphone which was easy to install in the factory location for a second mic. 

Carplay is wireless and appears to "just work" with Android Auto wired. One of the reasons we chose this unit was it uses the factory screen and doesn't require any overlays or touch screens. The factory screen isn't amazing but works fine and having true carplay and Siri on it is well worth it for us. Obviously it wasn't cheap but it works well for what we wanted.

I've decided to finish the job and add a reversing camera so will install that in a couple of weeks when it arrives.