For most no, almost all children(5-15) don't use it at all, but some older men use it a lot(40-80)
Do any men actually use the opening in underwear when they pee?
I've never been involved in (or ever heard of) a group of men discussing this issue.
My dad wore boxers, I have always worn briefs.
I don't use the "fly," but the boxers look like they "fly" option would be the best one due to their leg length.