Yes
Mandated by SCCA safety rules. Also a very good idea in RallyCross where bumps and ruts can cause big guys like me to clock our heads on the door frame. Not so sold on it for AutoX though...
Like: Safety
Dislike: Heat, uncomfortable to put on and remove (no comfort issues when on)
For the amount of time I wear a helmet, I'm willing to sacrifice features for affordability. Smaller size, easier on/off, and cooler temperatures while in a car might make me step slightly above my price point. But no $400+ helmets for me.
Honestly, if there was a way to certify a helmet for use in an enclosed car with no roll cage that was lighter and smaller, I think it would find a lot of popularity in amateur motorsports.