I owned a Rohent R7 HD 1080P RV Wireless Backup Camera, about $140.
I sold it for $50 after 4 months because I didn't like the signal dropping out. This was a 7" screen, not a rear view mirror. The small rearview mirror style cameras don't have a clear/large enough image for me.
Negatives I experienced, the weather (rain and snow) interferes with the signal between the camera and the screen. Signal drops out for a half second to 5 seconds. Using it on a 20' vehicle.
The image quality isn't as clear on wireless systems because a wired system transfers more data and produces a sharper image. The wireless video gets choppy, freezes, and cuts out all together when near large tower antennas (possibly cell or microwave towers), or some other remote unknown interference almost anywhere. Always worked great when in the middle of nowhere on sunny days, so there's that.
I know of a couple folks that love their wireless systems but they are on new motor homes and are in the $350 and up price range, beyond my wallet.
I now use a Transcend dash camera recorder and a commercial wired backup camera w/7" screen and both have work flawlessly over 4 years now.
I'm positive someone uses a wireless mirror system and loves it. Maybe they will post their positive and negative results here. I'd be willing to try again and use it for a side view camera with the mirror in the dash if the price was right.