I think the avalung backpack is a great idea, especially for backcountry skiiers, snowboarders, snowshoers, etc.
The problem with the avalung backpack or the avalung in general for snowmobilers is the dilemma of getting the avalung into your mouth if you get caught in an Avy. Some peeps say that when they high mark or are in Avy terrain they ride with the avalung tube in their mouth. That would work, but personally I would find that kind of annoying. So here I am talking you out of a product that I sell, doesn't make a lot of sense, but that's what I personally think. But if I were ever to get buried in an Avy, I would want an avalung in my mouth, I just don't know if I would be able to get it there with my helmet on in an Avy.
Or as was mentioned, save the extra $$ and buy an ABS backpack instead which will help prevent the need for an avalung