Never has a piece of equipment been produced that is such an utter waste of space. One of my dive buddies was convinced at one point that this was a must have piece of kit and thought it would come in handy in his Divemastering role, thinking it could be used as some sort of redundant air source.
Having tried one of these in a "simulated" out of air situation, admittedly in a cold water environment they fail to deliver the goods, a couple of breaths in a panic situation and that's it.
You'll see in some of the US Diving Magazines and agency publications glowing reports of how the dive proffesional musn't be without one.
Think Dominics link says it all.
