Actually, its for the QB who is only allowed to have that on when he is at the QB position...The rule was created to get rid of last second communication to the qb who may be a holder in a field goal situation.
SO, say he is the holder for the field goal unit, he cant wear that helmet.....
With that being said, cant wait to see the scramble when there is 17 seconds left, no time outs, going for the game winning FG, and the QB/holder has to change helmets to avoid a penatly......