I cant say enough about the Schick Extreme disposables for myself. I can probably use one for a month(both face and head, minimum once daily) and they work twice as well as Gillettes for me. Believe me, when I say that I have tried all the razors since I started shaving my head in 1983 and the Schick works best for me. Have never tried the HeadBlade because it looks like a gimmick to me and I'm afraid it would wind up sitting in a drawer.
I think blade life obviously has a lot to do with the softness of the stubble. Softening the stubble up first and using a good shave creme should make the blades last much longer. I really like the Headlube, and a little goes a long way.
Another aspect to this is water softness. "Soft" water gives a much better shave and will make any soap, shave creme go much further.
Anyway, being completely bald is MUCH chaeaper than having any hair. When you factor in the costs of haircuts, traveling to the Barbershop, hair junk, the TIME factor involved, having hair is much more expensive than being a chromedome.