Any shop teacher will tell you: Use a tool only for its intended purpose. But I confess—I often use a belt sander for jobs other than sanding wood. It works great to scour dried gunk off putty knives ...

I've been thinking about buying one of these but I don't know if they are just a gimmick. Also, if they genuinely work well how good do your bits need to be in the first place to be worth sharpening?