I did a quick search on Google and got 616,000 hits for rear view camera. Some are for mobile homes and are bulky and gaudy. Others however were tiny (fits the screw hole on the rear lisence plate). Some have units that are hidden in the dash and pop out like a CD player and then pop up for viewing. Several incorporate a tiny screen into the rear view mirror. Some color, some black and white, some use night vision.
I think they can be of benefit, especially for backing, if you are not going to use outside mirrors, and/or set them to eliminate blind spots.
In an earlier post on wink mirrors, I described how to set the outside mirrors up. Do it for your regular car first and see if you like it. It takes a little getting use to. It goes as follows:
Sitting in the drivers seat, lean your head against the window and adjust the driver's side mirror to the back edge of the car. Lean your head to the other side as far over as you did the driver's side and adjust the passenger's mirror the same. Now when you glance in the side mirrors they will look like they are way off, but what you have done is set them so that a car passing from behind will flow flawlessly from the center mirror to the side mirror. As the car moves further forward and out of the line of sight for the side mirror, it should be in your periferal vision eliminating "almost" all your blind spots. You might have to tweak it a bit. You should not have to turn your head to look over your shoulder to see if there is someone in your "blind spot" once set up correctly. Works great on the track. Works awful for those mirrors that tell you the object in the mirror is closser than it apears.
The drawback to this is when you try to back up, or if in a truck, tow a trailer. You will have to lean over to see the back edge of the vehicle or trailer. Electric mirrors would eliminate that.
For trucks, those accessory mirrors work pretty good if they are large enough. I had one of those tiny ones on my Lotus, Trying to change lanes at night, I spent too much time trying to decide if the guy in the next lane was far enough behind for me to change lanes, and ran up under the truck that had stopped in front of me. /ubbthreads/images/graemlins/shocked.gif
So as I see it, you have several choices for rear vision. "Pays your money and takes your choice"
Bill