Hello there
My friend and I make those blocks
We call them witch blocks as the "Witch" (Stefano from SDSS) and I came up with the idea independently at the same time.
For deep dives I use a 4 bottle system on my JJ. The reason for a large suit gas, is that in cold water the last thing you want is to not be able to get gas into the suit (over inflate) on deco and get cold.
If you're adding a bigger bottle you've now got extra volume that you can now use to inflate the wing. For me it's not about saving a few pennies on Helium, its more about the logistics of being able to do more dives away from a fill station (in this way I can get a week of 80-100m dives before needing a refill).
More importantly by moving the wing source, you can separate your wing and ADV (for both traditional 3L set ups and GUE style right post set ups). Folks love to fuss about putting two sources of inflation on 1 bottle, but IMHO fail to think things through as they usually have their ADV and wing together. The ADV is the supply to my most important volume (counterlung) and the second most important volume is the wing. So I'd rather have them separated. Suit needs its own tank as you can't inflate with helium unless you want to get cold.
It make sense to keep the wing inflator in place (from the 3L DIL in traditional set ups or the right post in GUE setups), as you can switch over supply if you run low on inflation gas (redundancy). BUT switching wing inflator hoses is easier said than done, especially in cold water with thick drygloves and under gloves on. We have seen quite some situations where people were trying to swap the hoses and got themselves in quite a pickle. Hence the reason for the witch block - Press a button and you can switch back and forth from back gas and suit gas to inflate the wing. Adding more orings for me is a red herring, since you can disconnect the hoses when ever you like and don't forget to mention the 100 other orings in the system
When on OC a loss of inflation is trivial (just inhale a bit) but on the breather you get large swings in buoyancy because of the huge ~10L volume of the rebreather and counter lungs. This volume is why you're flapping on your 6m stop, but means you can get crazy negative over just a meter or few in shallow water. In traditional or GUE setups you have the potential to lose the ADV and wing in one go and can end up descending quickly without being able to breath (ADV) or establish buoyancy (wing). You might say "ah just add to the suit" - which, seems pretty simple when you're sat in front of your computer but when you're over a wreck in 100m of water and your ear drums are kissing your tonsils whilst the loops tries to suck your lungs out of your mouth its not quite so easy.
So you want to get one? Kees probably has some in Seattle if you're in trump land, Dean has some in Ireland - otherwise send me a message (not here as my therapist said forums are bad for my zen)- my email is easy to find or Facebook (also easy to find). If you dive with SDSS you can get them from Stefano or Mario.
Graham
