I use a DE every 2nd day (or so) for my head. Have tried the straight for this but find getting the angles right for XTG or ATG around the back are a bit tricky.
Shaving your head with a DE ( I can actually imaging doing ) but a Straight Edge?? I can't imagine!! I used a Mach 3 for at least 8 years or so to shave my head. I can't remember how many passes I would do... anyway. Straight Edge+Head=Brave