The concept is to make an avalanche victim that tennis ball. Increase their surface area enough that they end up on top of the avalanche with the other big pieces, not buried underneath them. This has proven surprisingly effective, with over 500 simulated incidences using dummies and explosive-released slides, and a handful of real-life incidences. These bags appear to double a victim's odds of ending up on the surface.
The con? These bags are heavy - I only use one riding in the sidecountry, or with mechanized assistance. The manufacturers know this though, and I expect to see bag weights drop considerably this season. Cost is another - I know, "How much to you value your life" and what-not, but fact is most consumers do put a price tag on how much they'll pay for security. Finally, they can be complex, and require refilling or replacing a canister after use.
This is pro snowboarder Meesh Hytner, on 25 January, in the Snake River backcountry near Montezuma, Colorado.
Because of the weight/space penalty, I still haven't justified carrying one all the time. But you can see the train a-comin'. The video of Hytner went viral, and a wave of internet criticism came out against the decisions of the rider, the team, and surprisingly against BCA for showing a video of its product in use. Some even claimed that it was staged for marketing. BCA ended up issuing this statement in response.
Arguing that avalanche rescue equipment encourages reckless behavior is like arguing that driving the safest car on the market encourages speeding, fast lane changes, and cutting other people off. Of course it does - to a point. But in the end - its up to the rider. Or the skier. Or the sledder. Not their equipment. Having one of these packs doesn't replace a shovel, prob, and beacon (for the short-end-of-the-stick odds of ending up buried). And having all this gear doesn't replace good decision making.
Disclaimer: I do work for BCA as Technical Representative. The views expressed here are my own, and don't represent the view of Backcountry Access.