Yes, I agree to this, if you are confident to swim up from 30m with your equipment, keeping the airway open is hardly a skill, so, freediving will surely prepare you for CESA or increase your safe ascent probability.
At the same time, I do not find redundant air supply discussion very relevant, pre-condition for CESA consideration is you already exhausted AAS or RAS options, I mean you can breath your pony empty and still having to do CESA anyway.
I remember reading that, in a lot of OOA related fatalities, weights were not ditched and I think this could be related to the fact that most of the divers consider buoyant emergency ascent as much more theoretical option. To consider CESA or BEA risky is a risk on its own imho.
With 30 meters OOA situation, you must be prepared to ditch the weights because you are more in uncontrolled emergency ascent territory. This is the reason I find practicing CESA from 30m unnecessary; you ascent as much as you can and you ditch the weights whenever you cannot take it anymore. So practicing cesa from 5-10 meters is sufficient. Question is whether you will take the decision to start to ascent or even ditch your weights on time. Improving in water skills such as free diving will give you the confidence to take that decision when **** hits the fan.
How do you do that?
If you bailout, you
only have two decision, do you ascent immediately (alone), or do you ascend with your buddy as soon as you have attracted their attention (with minimal delay).
The only time I have seen a Pony breathed almost dry (empty)[1], is when there where multiple failures. A team of three lost two first stages.
Diver A had a free flow (first stage iced up), and went on to diver B's AAS, starting the ascent. Diver B had a free flow (first stage iced up with the additional gas through put). Diver B went on to his Pony. Diver A went on to diver C's AAS, diver C switched immediately to his pony. Diver A and C blew the stop and ended up on the surface, Diver B did a stop, almost exhausting the pony [2].
(Fresh water 2C, 35m, surface temperature below freezing, back in the 90's).
Thats when I decided that it was a really good idea to have a pony, if I was going to dive in the UK.
The size of the bailout is related to the depth and type of dive being undertaken.
My rule of thumb, below 20m a pony, shallow penetration a pony, below 35m a twinset. Recalculated if significant decompression or penetration is intended.
In the failure I witnessed, the pony's got them shallow enough to complete any required decompression and safety stops (Diver B).
I've been in the water a few times, when people have bailed out.
In fairness, even if you breath the pony dry, you are closer to the surface than you where when you initially bailed out. So your CESA is going to be easier - you might even have some methane power in the drysuit by then!
Gareth
[1] I have seen pony's breathed dry when they have been used as deco' cylinders.
[2] Funnily enough diver B was a paraplegic, an ex clearance diver who got blown up by a mine. Every one was freaking out that he was still under water (on the stop). When he surfaced he was as cool as a cucumber. Pointed out that with or without legs he was in no danger!