This may be the winner for the most intelligent dboard discussion ever.
A helmet will never prevent a concussion. Concussions are a physiological response to trauma when the brain impacts the skull due to impact or rapid deceleration of the head. Helmets are better suited for protecting the skull from fracture due to direct trauma. A manufacturer's claim is more a marketing bullet point than science
The "A helmet will never prevent a concussion" guy always posts on this topic and there is substantial evidence this guy has been wrong forever. Maybe he is a Bauer 4500 'concussion bucket' wearer for years.