I think their argument is that, for the double impact, neither impact can transfer more than 300 Gs. Now, I don’t really know how much force that is, in terms of head injury. But if 300 Gs is below this threshold of injury, then I support it being able to reduce the force two times in a row. To use your analogy, if the vest can stop a more powerful bullet, why not try to make it stop two of them. As long as we’re sure that it can stop the more powerful bullet, which I think is the bigger issue here.
I don’t know. I’m not a physicist, nor am I an expert in blunt force trauma to the head. I think that most helmets on the market will protect your head just fine, whether or not Snell has anything to do with it.
It’s an interesting question though. People say that Snell has “stricter” standards, but there’s always a trade off.