Speaking of the fibreglass(?) helmets (i don't know the material that is used to make these) covering the top of the skull with a strap dangling down (which are not strapped many times), do they serve the purpose of protecting the head? When the straps are not clipped together (perhaps, even when they are in place), there is every chance that the helmet could slip off with a strong jerk of the body? These helmets seem fragile to me.

Seriously, people should use the ones which covers the entire head, with a visor in front. Atleast the head is protected to quite some extent by these.