I agree with degraw I shave my head every other day or so, with shaving cream and a mach3. I've also bought electric razors, but they are more time comsuming, and you don't get a great shave out of them, and yes.. they won't last as long. If you plan on shaving your head on a weekly basis or more, then use a razor.. if your interested check out this place
HEAD SHAVE CENTRAL they have alot of good info there..