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?

Bver tried to cut something with a pair of dull scissors? How about shaving with an old razor? Cutting or trimming with anything that isn't as sharp as it's meant to be is no fun-and the same goes for ...