RWB
You're quite right when you say that an S76A+ won't fly away but you don't mean CDP or TDP. Both of those terms refer to Class One performance and anyway are both different names for the take off decision point. Most helicopters (except possibly the AW139) are usually too heavy to be operated Class One offshore and most S76s that I know of are not modified for Class One elevated heliport operations.
I too have worn a helmet for military operations and some civil operations, but I chose to wear a headset where I work in Africa. Some of our pilots out here chose to wear helmets. I guess it all comes down to whatever you like and what you personally judge the risk to be. As for wearing a headset because you might hit your head on the overhead console - speaks of not having the seatbelt properly fastened!