I got a bundle of cameras in my car, all just recording.
No monitors needed as i have windows to look out of, and i dont have a reversing camera or a screen to display its footage on ( 2 DIN headunit "broken" and wire harness missing )
I once had my 4 channel DVR connected to the then working headunit, but its just a gimmick, surely not something you can use while driving, and stopped, well you can just use your eyes maybe turn your head.
Though i must admit turning to look are getting more and more problematic for me and my back.