Aftermarket backup camera?

What do you know about aftermarket backup camera systems? This would be for a grandma, so simpler is better. 

I put one on my daughters first car.  Camera mounts above license plate and gets power from reverse light circuit.  Monitor sits on dash and either has a wire all the way back to camera or has a wireless signal.  Power comes from plugging into cig lighter or another power source.  Monitor turns on once reverse is engaged.  Screen is same size as her Garmin GPS.  Whole thing was a big deal for my wife.  She was worried about the kid hitting something.  Pretty much a waste of time and money, at least in our case.  Kid was scary while she was learning to drive, but now she drives like a pro.  One more thing she takes after her dad.

Many modern head units have backup camera inputs and will automatically switch to that input based on the reverse switch.

There are cameras that mount to the license plate and there are wireless camera adapters to avoid having to run the cable.