helipilotnz,
If you want to wear a hemet go for it. I have done almost all of my training in the Gentex SPH-5, in a R22. Alot of people at the school made fun calling it a crash helmet (like I care), but I wouldnt fly without it. Aside from being more comfortable than any headset I have worn, I feel better for the wearing.
I read a stroy about an Ag pilot who clipped a fence while turning around at the end of one run. As he realised what happened he shut the throttle and prepeared for impact.
After he came to he found he was unable to move his head, undid the strap of his helmet and pulled his head out. The entire weight of the helo was being suppoted by the helmet after rolling over. Needless to say he would have been severely injured at best without it.
If I was told I coulnt fly with a helmet Im not sure that I would. The majority of injuries from accidents in aircraft are to the head.