I had this installed yesterday on my 2021 230i, which comes stock with CarPlay but not Android Auto. Here are my thoughts so far, which apart from (4) below may be as much about Android Auto and associated overhead as they are about the MMI Prime hardware and firmware:
1) Happy with the USB connectivity, need more time with bluetooth to evaluate. I did have to reboot the phone after a service station stop on the way home from the installer yesterday, but that may be unrelated to the installation.
2) BBC Sounds, Waze and Cloudplayer album play all working well, although re the latter I may download my FLAC music files on MS OneDrive to the phone's storage as there have been a few momentary drops (fraction of a second) over air. Voice commands in Waze working well.
3) Cloudplayer Magic Radio unable to maintain a steady connection on BBC World Service for instance, but installing Sounds as an alternative seems to have made that issue moot.
4) The installation does require a USB lead to protrude from under the radio pod in the dash -- the installation cannot use the factory USB port. In other words, there's a fair degree of integration (iDrive etc.) but it is not complete.
In summary this should be very useful, on long trips especially, pending some time to see how solid the overall installation (hardware and software) turns out to be.