repair would probably be OK, bearing in mind the relatively light damage in a relatively obscure area of the bumper.
make sure you use a repairer which uses the Mercedes "paint system" -- it's Glasurit, I think. This ensures that the paint matches perfectly. When my bumper was first repaired (and when I knew nothing about paint systems), the colour match was terrible.
Whats a 'paint system'? I got a Mercedes sport pack sprayed by a local indi. It was an almost perfect match, now considering the car is 6 years old I think thats a pretty good effort.