I had one of these a couple years ago. It worked very well for a few months until winter hit... I'm not sure if the cold did it in or if that was coincidence, but it refused to stay stuck after that. Kept falling off, no amount of cleaning or re-positioning helped. I really wanted it to work but didn't have nearly as much luck as most reviewers seemed to. For the $16 or so it cost it was worth the gamble, but I came up a loser on it.
As for 'stop using your phone while driving!' I though the purpose of these was to let you use the navigation on your phone without trying to awkwardly juggle it in your cup holder. Helped a ton with that while it worked! No different than having a TomTom or Garmin mounted.