Has anyone used portable backup cameras?

A few years ago I almost bought this one. I saw it was recommended by a few RVers. It uses your phone as your display. The camera is battery-powered and attaches by magnetic mount. Make sure you find the steel sections of a trailer. And it is wireless unlike the bolt on backup cams that attach to car license plates that require a wired 12 volt power source.

 

The tanker trailers I was pulling are aluminum.
I only would have needed the cam for about 1% of the locations I back.
It's kind of expensive.
You still have to get out and attach the magnetic cam or leave it attached and risk it being stolen or falling off. Or drive off with it attached to dropped trailer.
Van & reefer trailers only have steel in a few inconvenient places to attach the cam.