One thing to remember (don't ask me how I know)...
The inexpensive "back-up" camera's are not intended for continuous duty and will, I'm told, burn out if left on too long. That's why those cheap camera's are wired into the reverse (back-up lights) power source.
Mine has already gone out once, and I was amazed how tiny that the actual camera is... about the size of a nickle.
When finances permit, I'm going to get an actual rear view camera.