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Get the battery powered one, and get a 9v 1amp wall wart (it can run on batteries or the wall wart).

Also buy spare sanding wheels, at least 3, preferably 6.

Source: I have one. It takes 2 minutes to do a full pass. One wheel will do about 100 discs before being too worn out.

Of the ~200 unreadable discs I've run through it, perhaps 5 were still unreadable afterwards (and those may have had a copy protection failure, I'm not really sure). I do know pretty much all were readable afterwards, when they weren't readable before.

Edit: the spray is just water with a drop of dish soap. Use lots of water - when I hear it slow down I know it needs more water on the disc, so give it another shot of spray.