I would have to agree with the previous comment. The ABS bag is the only device, of the 2 highlighted, that is design to keep you on the surface of a moving avalanche. In fact it is the only one that is officially recognized as a preventative safety device. The avalung will not keep you from getting buried, the ABS will. They are way more benefits from using a device that prevents potential burial than not. I would definitely recommend the ABS over the avalung to anyone interested in investing in this new technology.
The ABS bag industry is booming at the moment. There are so many options available to the public. With such a trend, packs are getting lighter, designs more refined and the price more affordable. There is no question that the ABS packs are heavier that the avalung however, the ABS system is incorporated inside the backpack system. Below is a link to an interesting study comparing most current ABS packs currently available on the market, it is very informative:
Few more thoughts; with all this new technology available it is becoming increasingly difficult for people to make rational decisions in avalanche terrain. It seems that people are willing to take more risk because they are less likely to get buried. This is increased risk tolerance is sometimes very subtle, it is a very dangerous line to thread. This could be a whole different topic of discussion.
No matter what safety device we use, I think it is important to make educated decisions that will maximize our chances of survival. The ABS bag will obviously do that however, it is does not mean you have to push the envelope even farther.
Have fun in the inter-season!
ACMG/IFMGA Mountain guide