The camera came pre-installed on my car, so I don't have any comments on installation.
Not having really lived with a car with a back-up camera, it is immensely useful to me. The camera is completely hidden while normally driving and sitting in the car, but when in reverse, the screen pops up in the rearview mirror. The camera projects two "aircraft landing" lines on the screen, to align your car with spots and curbs.
It is indeed an expensive dealer option, but I definitely appreciate it every day. I back in everywhere perfectly, I can see low jutting objects such as curbstones or debree in the way, and I could imagine it would be invaluable if I ever decide to lower my car. Of course, you could get away with good practice and knowing the dimensions of the car, but we all make mistakes sometimes, right?
