We bought half helmets when we got SS. Figured it would allow us to hear each other when traveling and it has. Haven't put a helmet on one time since we got the Bullet Speed Top. Keep them on hand just in case we get stopped. Gonna get us some full face helmets when it gets cooler.
I will say that with the slingshot as my daily driver having a full helmet for the cold and or wet days is a nice thing. Not only does it keep your head dry, but rain hurts at 70 mph