Hi all, new to snowwest and liking it a lot so far. Need some input/advice about avi packs. I've been reading a lot about them and I believe I just have to make a decision. I want one as a safety fall back, besides making smart and safe choices on the mountain, but I really don't know what to buy. First off I've heard some negative feedback on the compressed air models (BCA) vs. the nitrogen models. Is there really a risk of lines freezing up with air models and the bags not properly inflating? Second, are two air chambers better/safer than one? Is having a similar model to the group you're riding with smart so there are numerous extra refill tanks? I'd like to get an ABS bag but they are harder to find used and more expensive. Is one really better than the next? Thanks