I've never used them, but have always been skeptical that they were of much practical use. First off, you can't thread them through very small openings, so you are limited to where they can be used. Second, I think it's best to focus on using the proper blade and practicing your technique, so as to eliminate the need or at least significantly minimize the amount of sanding required. I do use some small files, with various profiles, to clean up some areas that may require a little tweaking.