MIPS is more than just allowing the helmet to move a bit when you crash. It's also about reducing rotational weight and stopping the heck from getting whiplash by lightening the helmet altogether.

However, MIPS isn't for everybody. If you are going REALLY fast or riding REALLY hard, if you crash the MIPS won't help you any more than a normal helmet would. Once you "max out" the helmet, it acts just like a normal helmet, since you've reached the limits of the travel for the shell relative to the mounting parts. I'm paraphrasing from someone who runs a bike shop and saw all the new MIPS technology at a bike show earlier this year.

Also note, MIPS will not help you any more than a normal helmet in terms of a concussion. They don't have any more or less padding/foam than a normal helmet.

In all honesty, I think MIPS is a solution in search of a problem. However, it'll probably be on all helmets in the next couple of years. If you're crashing hard enough to hurt/break your neck, the main thing MIPS protects against, you're going to still hurt/break your neck regardless of which type of helmet you're wearing.

Please note, while I don't particularly support MIPS, both my helmets have it. Not because I wanted it, but because I didn't have a choice otherwise. (I bought expensive helmets.)

Also, how the heck does MIPS work for full face helmets? There's no way in heck that my full face would slide in any direction without taking half my face off. That's the point of a full face...