^^ What he said. I can see this working for casual riding on a comfort bike.
I'm not sure about higher speed collisions with vehicles, but I'm seriously sceptical about using it off road. I can think of some cases where there wouldn't be enough sudden change in movement but head protection would be required (e.g. clipping your head on a tree or rock on the way past) as well as cases that might activate it unintentionally. And I'd like to see more details on how long it takes to activate, from deciding you're crashing to being fully deployed.
Skiing/riding probably exhibits a totally different movement pattern and I doubt there is such a clear distinction between crashing and not crashing in it.
That said I would love to see more C-spine protection for snowsports and if this prompts people to look into novel ways to achieve, cool.