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?

Sharpening a drill bit is rarely a second thought for most DIYers. It's straight out of the case, into a chuck and start drilling. But drill bits are not indestructible and are prone to wear and tear ...