Richard, the guys that have used both the suction cup and the 3M stick on mounts seem not to have any problems. I tried the suction cup and tied a lanyard to it just in case but didn't need it, it stuck fine. The only downside to the stick on mounts is they seem to be pretty permanent. I am probably going to buy one of the POV.1 units from Jim Gustafson, so I am reluctant to stick one of the permanant mounts to my bodywork.
I think the best location is behind the driver over a shoulder. I think being able to see the head movements and the dash and steering wheel add a lot of perspective to the video.