Spare Air is and does exactly what it claims to do. That is to give the diver a margin of safety which exceeds not having it. In response to the divers who want a 13 cuft pony or a 40cuft stage bottle, hey why not dive doubles? The fact is, most divers will ascend with at least 500psi still in their tank. After all, that is what we were taught to do.
Why then carry a Spare Air? It gives one the extra time to get to their buddy if sharing air is the only alternative to making a safe ascent.
Divers should, with proper training be able to make a safe and controlled ascent from a non strenuous dive at 30 ft on a single breath, while exhaling the entire way up. Many seasoned divers can make this ascent from a depth of 80ft or more. Of course this omits the safety stop, but years ago, we never heard of safety stops.
The bottom line, a Spare Air is better than nothing. I would rather make an unassisted, independent ascent, than rely on a buddy ... especially one the boat captain just happened to assign for the day.
Most of us travel to remote dive sites and dive on charter boats.
These trips may involve flights with 2 or more change of planes.
There is no way I'm going to be able to do this in today's world with a 13 cuft or larger pony/stage bottle. I know I can place a 3 cuft Spare Air in my checked luggage, so long as it is not pressurized.
No arguments here. I carry a Spare Air all the time. I've NEVER needed to use it. I have experimented and found it quite adequate to make a controlled ascent from 80' without a safety stop. Having dove conservatively, this does not create a problem. Please, don't hit me over the head. I am not preaching to omit safety stops .... I am saying that if can be done if you must. And, if you do, you might want to omit diving the rest of the day. That's your decision.
For you die hards who like to carry a 13, 30 or even a 40 cuft redundant supply, remember, you're sucking more air and working harder dragging this around. There are times I'll nest a 40 between my twin 120's but we all know that's not the norm.
So get real, this guy has made a conscious decision and should be applauded for it.