I've used Dr Colorchip with mixed results. On a flat black Alfa GTV it worked pretty well. It's sort of a great thing to do before selling a car as it will improve the appearance but you can definitely still feel the chips so it never feels (no pun intended!) like a proper solution, more a half-way house one. If you really want the chips gone you have to repspray; if you just want to improve the appearance it's worth a try. Go easy on the bottle of solution they provide to wipe the excess away with as that runs out fast but you'll have stacks of colour left. :|
I also tried Dr Colorchip on my silver grey M3: complete waste of time on that colour unfortunately; in my experience some colours work better than others...