Check with the organizations that you’ll be racing with. Looking at the USPKS 20015 rules, because I just downloaded them, reads that the Leatt-Brace Moto Kart and Moto GPX are legal for this series.
LAD Specialties customer / tony kart / rotax / kt100
Josh, yes they offer a good deal of movement, BUT they are intended to stop TOO much movement!! Your neck will move, but hopefully not so far as to break it. I love mine, and have been using it pretty much since they were introduced. Also a deal with my dear Wife, she said “Get one or quit racing, you’re too old to break your neck”!!! Not that it’s OK to break your neck when you’re young, –just sayen’!
My Daughter uses one of these, I think there the best on the market IMO, and Clark is right they are designed to allow movement but that movement can be adjusted to give you more or less movement. Have you adjusted it per the owners manual? There are a couple little allen screws that will let you adjust the amount of movement more or less and once you get it right you lock it down and never do it again. Just unlock the latch and remove it.