I've done them for 18 years, clicked easier than regular ones for me. It's a rare trick but I've met many people who could also do it and just never would, also it's made a little resurgence in videos recently (I guess a few years after the impossible resurgence it had to) but it's an especially hard one to throw down or over stuff which probably explains why you practically never see them unless sometimes on flat. Mullen was doing them nollie in Future Primitive and that was in 1985. If you doubt that such tricks have been done, then you're seriously underestimating what's been done on skateboards for the past four decades.