the wireless one is a little fussy but if all you are doing is trying to hitch a trailer then it should be fine
the rear view mirror one is a little better, you hang a screen type rear view mirror over the existing mirror and it puts the picture up in a little square on the mirror
but if you really want to get a good view then you will need one with a fish eye type so you can see from side to side, then you are looking at $700 for the camera and little monitor
you can get a great system from Pioneer that has a backup camera, GPS, DVD player, radio, etc type model for about $1000