I have a 15 year old a 10 year old and a 10 month old...all boys. I dont need a stupid conversation mirror to put them back in place whenever the (very seldom) occasional fight breaks out in the back (between the 15 and 10 year old). A simple repremending with a raised voice while keeping my eyes on the road is enough to get them back in line.
As far as my 10 month old, if he is quiet then he is asleep. If he is playing with his toy, talking gibrish, and/or crying, then he is awake...very simple, dont need a damn mirror for that either.
C'mon people (that use or want a "conversation mirror") stop making excuses about wanting or having one and just simply teach disipline to your kids and teach them who's the boss, so a simple repremending will put them in place.