The nail file driver does work quite well for what it is. There are a couple variations that I like even more. One is a Gerber nail clipper/SAK-like classic. The nail file driver tip is is essentially the same shape, but not buffed smooth. The sharp edge angles just seem to work better at "biting" into screw heads, and better at cleaning nails, too. A similar tool tip is found on this small Mantis keychain knife I have. Folks around here get pissy about that company, but that knife has absolutely flawless fit and finish, and the flat/Phillips tool tip combo works better than any other I've tried.
I've modded my favorite Wenger Esquire nail cleaner so that it has a similar profile as the Mantis flat/Phillips tool tip. Much more useful, IMO.