I see having QC whips on all stages as expensive and adding risk of failure (hose or QC) preffer to KISS
I have all bail tank 2nd stages fitted with p-port adapters which i slide a normal apeks mouthbite over in case someone else needs to use it. (actually you can breathe straight from a p-port adapter its not comfortable and you feel a big gay but its doable in an emergency.
The mouthbite also protects the o-ring
In event of a bail I plug them in to my main p-port (i dont use a bov as with the side reg I dont see the need)
I have a maniflold with three hoses, one goes to a QC by my left side hip which I connect my deepest bail tank to, one goes to my wing and the other to the side reg.
I agree with Matt re:using QC in stressed conditions (or with frozen hands)
Im using swagelok QC6s - Id NEVER rely on APD QC for critical appliaction! been there LOST all that gas
You need to ensure the QC can give plenty of flow as your relying on it for primary bail. This is one reason I like to use standad 2nd stage as bail. Doing that I only have a single hose between me and gas supply, no elbows, no QCs, no Y pieces. Max flow rate gas and KISS.
Something else to consider, as Matt will tell you, when were doing one of our deep cave expeditions we usually have lots of stage tanks which we beg borrow and steel regs from wherever we can get them. People dont like you pulling off their mouthbites and adding p-port adapters and Im not about to invest in and carry around with me a dozen or more QC and hoses so what I do is just loosen the borrowed 2nd stages so they are hand tight (mine are all set up this way too) then if I do need to use those stage tanks (after Ive breathed all my p-ported ones empty) I simply swap 2nd stages with one of my p-ported ones underwater. In next months exped we may have 12 stage tanks plus ones Im carrying. The ones Im carrying will be p-ported - the rest likely not as they wont be my regs so I use the above method. The idea is when youve emptied the p-ported ones you should be well into deco = calm and no rush, at that stage you have plenty of time to swap 2nd stages. Having hand tight 2nd stages is also great when you get free flowing reg or bad breather (cos its full of clay
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And of course if all this crap with mask, p-ports etc etc all goes tits up, I pull mask off, don my normal mask (which I carry in pocket) and use standard 2nd stages (or p-ported ones with mouthbites pulled over)