It seems the fewer number of blades, the less chance of getting irritation. I can be quite aggressive with my DE safety razor, a little more careful with a 3 blade, and for me, the Headblade just didn't work well.
I think one of the fun things about headshaving is trying so many different razors and products. Even after you find the best equipment that works for you, it's still fun to find new stuff. Every time I read that sporting a shaved head saves you money, I have to chuckle a little.