I can't address the effectiveness of the nutter itself as I've never used them. But I have used several styles of oversized blunts like the HTM blunt, Black Diamond Shockers, and washers behind field points. You'll definately lose squirrels with these types of heads.
I'm still looking for the perfect squirrel head, but until I find it the bladed blunt (whether homemade or boughten) is by far the best. With squirrels I think it is important that the arrow stays in the animal. Helps keep'em from getting up a tree and out of reach before they die. And unless you make a direct head shot (in which case type of head is irrelevant) they will have some life in them for a spell.
Broadheads alone generally won't stay in the squirrel, many times will zip through a squirrel without knocking it out of a tree, and even with a solid broadhead hit they can get somewhere quickly where you can't retrieve them. Also very dangerous to be shooting these heads up in trees.