Crap Cleaner and Scan Disk are two very different thing.

Crap Cleaner simply removes a bunch of files that you most likely don't need. It saves space on your hard drive.

Scan Disk actually verifies the integrity of the file structure. It makes sure that all of the files are the length that they are supposed to be, checks for cross-linked files, and frees up clusters marked as allocated, but not in use by any file.

Both are good programs, and neither one can replace the other.