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?

Knowing what tool is used to sharpen knives will save you a headache when you find that yours are becoming dull. Most of the time you don’t need a power tool or an expensive knife-sharpening system to ...