These work very, very well... at least in certain situations.
I do a lot of platter cleaning. When I read this post I was working with a dirty top platter of a 2.5" Hitachi. For something that should have taken 5 minutes I ended up spending at least 4 hours total on it and was only able to do a mediocre job... the ISO would dry into huge residue smears behind the wipe instead of "pull" along with the wipe and leave a spotless surface. Sure, you're always going to get nasty smears when swiping across media damaged areas, but this was a platter with only debris and absolutely no media damage.
After I developed a technique using the donor for this case, cleaning the entire platter on the patient took 60 seconds (using the same swab I cleaned the donor with).
Tried a swab on another case today--3.5'" WD. Platter securing ring had been grinding against dented-in lid. Contamination all over the place. Swab worked pretty well but I was able to do a better job, and more quickly with my normal method.
I will definitely keep a ready stock of these in my toolbox.
