I have these in two of my cars (both Audi's) and plan on putting one into my M340 when it arrives. Definitely stealth install but no third channel. If you connect it to the wiring harness in the mirror (usually picks up off the rain sensor) then unfortunately you don't get parking mode, but if you hard wire it back to the fuse box you do.
Image quality is very good, pretty much as good as the Blackvue 900x I have in another car, though the app is rubbish by comparison though.
https://fitcamx.com/collections/bmw