I think futa is only ok if testicles aren't present, cause all it does is hide the most important part from view. Anyone who draws or adds in the testicles to futas are probably just secretly gay.
example: bible black and star jewel did futas perfectly. no testicles
Futa is more of an American thing nowadays probably cause most of them have yet to come out of the closet, the japanese medium get a lot more creative with their ideas.