CD care - cleaning and scratch repair

Does anyone here have any opinion of CD cleaners and scratch repair kits? In particular, how effective are the mechanized units? (hand crank operated) Any brands particularly effective or ineffective?
So far the Disc Doctor has successfully repaired three discs that I loaned my son. They ended up in the floorboard of his car. even so, they were not totally trashed, some of the songs would play. Now all of them play.