In reply to Martin McKenna - Rockfax:
From the road.cc website:
"Do you need MIPS? Using careful evaluation, and in light of Snell testing showing no benefit in their test configuration, we are still not convinced that you do. It probably won't hurt, other than any effect on ventilation, of if your manufacturer has kept the same outer profile and reduced the thickness of the normal liner to accommodate the MIPS layer, or if it lets the helmet slip too much, or if the extra cost of the MIPS model makes a difference to you... We think the jury is still out on MIPS."
https://road.cc/content/feature/all-you-need-know-about-mips-252931
Here is the Snell testing:
https://helmets.org/mips.htm