I know it's probably been mentioned on here before but I thought it worth repeating now that I've used it myself for the first time.
It's absolutely bloody brilliant! My 13-year old Neff double oven looks almost brand new, I'm not exaggerating.
It is fairly labour intensive though (I took the oven shelves outside and hosed the product off, couldn't really see any other safe way to do it) then spent about an hour in total wiping down both ovens until the water ran clear.
Hardly a mark left, and the shelves are pristine!
Must get a life for Christmas 