I'm not a big fan of the MB ones and prefer the ones that beep with varying intensity as you become closer. MB ones beep about a foot away which is bit late unless you're driving very slowly.
I have just received a new W205 Estate. I agree about the sensors only giving a beep when a 12 inches away from an obstacle. All my previous cars have starting bleeping quite a distance from the obstacle and increase in frequency as you get closer and closer. I prefer this as I can look around me and be confident that I am not about to hit something instead of having to continuously watch a bar graph on the display. Also you don't get any surprises if you are approaching something you can't see. A bleeping some distance is a better warning than a single bleep when you are about to hit something. A foot is too close to react and hit the brakes. Hate it!