ok here it goes
i got a leatt adventure pro about 3 years ago, the first few rides were a challenge, just because it was one more thing i had to get used to while riding, but after that, i haven't noticed it since, it does offer a bit less head movement than without one, but i'd rather use it and not need it, than need it and not have it.
my dad recently got a alpinestars neck brace, i did notice that the astars one is a little lighter than the leatt, it also allows for a little more head movement than the leatt, in my opinion if i could get one, i would probably get the astars over the leatt, just for the lightness factor and the a slightly more movement. But both are good, and i would recommend either of them to anybody willing to get one