I got one of these - http://www.ribcap.ch/en/online-shop/cap/jackson_marine/jackson to try out.
comfortable, snug fit feels like it should protect your head well, though have not tried out the falling off the bike bit as a test.
Only gripe, Sweat inducer. It has a Merino wool/Acrylic material that is warm added to heat from exercise, Very warm. I will not be using it unless it is below 1 degree C. I had to towel down after use an it's about 3 degrees outside. They could have got away with using a cooler material.
The wife says she wants one, but excess heat has never been an issue for her.
So Good product, but not if you expel a lot of heat from your head.