Having ridden powerfull motorcycles before helmets became compulsory (wore one most of the time anyway) and come off a few times, I can understand the necessity of protecting the box that houses that part of our being that says "Go land yachting and I will give you huge sensations of pleasure."
According to an article published in "Two Wheels" magazine at the time, debating the pros and cons of "skid lids", "brain boxes" etc, the maximum speed to stop impact the human brain can withstand is 24 kmh.
You pays your money and you takes your chances.