Just got my Air back from the CCCv2 install. As advertised, much faster response from the touchscreens. Loading of playlists in Spotify and Tidal are improved as well. The most interesting and surprising improvement is how much better surreal sound pro is. The car was completely reset, and bass, midrange and treble were in the middle. It now has a much better distribution of sound from all the speakers.
As for the downsides, as previously mentioned, everything was reset. Had to recreate the profiles, pair phones, pair mobile keys, log into all the streaming apps and reprogram homelink.
If you are keeping your Air, highly recommend this upgrade!