I got one shortly after posting this.
It restricts some movement, was weird at first, last summer I noticed it was hot, but last fall I was hit from the back at a hare scramble, we were really ripping down a fast section, maybe close to 40 mph, went over the bars, landed head first, I know this cuz I watched the world turn upside down, landed on my head, I cracked 3 vert in my back, that's bad, but I'm sure it I wasn't wearing my neck brace I'd be typing this with my tongue!!!
My advice you can never wear enough protection out there!!
Joe :)