Not that it correlates much to every day driving, since both speeds and driving patterns differ, but e.g. NASCAR drivers wear helmets (along with that whole neck protection setup that latches to the helmet).

I don't know, however, if a helmet may work worse in conjuction with an airbag though. So personally I think I'd stay away from helmets in cars (but I really have too little data to make an informed decision).

Having said that, in the case of this company, perhaps they could offer their passengers a "Hövding" device? (Hövding being the swedish word for a chieftain, but "hövve" is also slang for head, and in the case of this product it is a... "backpack/necklace thingy" that is a wearable airbag. Supposedly works really well, but probably comes with a price tag matching this function.