I've tried a variety of different leathers, and one or two layers. There seems to be a difference not just on how kind it is to your fingers, but where the arrow impacts.
One layer of cordovan or cowhide with the hair on gives me the best shot grouping, while two layers will give more protection to the fingers. It seems that a stiff tab, or two layers, or a leather with a high coefficient of friction, will result in the arrows impacting in a larger group and generally to the left of the target.
This opinion is not completely on line with the topic but I thought it might be something to consider before cutting up a good pair of boots.