Many years ago, one of the magazines how a great in depth article on helmet safety. This was before MIPS for sure. I thought I saved it but alas, I've never been able to re-locate it. Anyway, the short version is that according to these researchers, the USA/Snell standards for MTB helmets was too high....in a way saying that the helmets are made so hard/stiff that they were actually causing concussions. The article said the European standards were safer in that they allowed the helmet to crush easier to dissipate the energy more effectively leading to less concussions.
I've personally been a Troy Lee fan specifically because they fit my head the best. I have a couple A2 models. Surprisingly, their super popular Stage full face is terribly uncomfortable and I wouldn't wear one if it was free.