I did not like slinging for many of the same reasons. Passing bottle off to a diver who has become entrapped is a plus though.
My backmounted valve is always open and the second stage and spg are right where I can see them, always.
My backmounted valve is always open and the second stage and spg are right where I can see them, always.
While I do sling my bigger bottles, I tank mount my 13 which I use for recreational dives in the 60' - 110' range - or when ever I am lobster hunting.
As far as reaching the valve, if you mount the tank upside down the valve is easy to reach, I am not sure if you tried that orientation. Also as I noted I use as Scuba Pro (cinch strap) to mount the pony. This makes it possible and actually, quite easy to remove the pony from the tank even if your BP & Wings are still attached.
Just another note. For all my single tank BP & Wing rigs. I use a standard ALU buckle(in my case the older style DR cast ALU) cam band on top and a SS cinch strap type band on the bottom. This makes it much easy to mount your ring on tank - no need to slide the lower strap down the entire length of the tank. Much easier to remove as well. Also when using a tank mount pony you can attach the pony first and then just drop the BP over the tank, buckle the bottom and then tighten the top band.
As I noted when I am diving with 30 or 40 cu. ft. bottles I always sling them on my left side.
I own both sling and tank mounted 19 cuft (and a couple of 13 cuft for shallow dives) ponies. In real life situations, I believe that a person will just grab for whatever they can get. Since they are out of air, they will have difficulty inflating their BCD for ascending to the surface, so it is likely that I will be controlling buoyancy and hopefully calming my divebuddy. I really don't intend to hand off a pony to anyone. In all actuality, the pony bottle is for me in case of failure of my primary system. Hopefully, I won't be careless in monitoring my air.
I do a lot of hunting and crabbing, which takes me to the bottom. I have found that the slung pony is in the way and gets all scratched up.
With my 19 cuft tank (upside down) mounted pony, all is out of the way. While I can turn it on and off while it is mounted, I dive with it on so that there is no messing around in a panic. The secondary is on a long hose (loose hose bungie corded to tank) with a parallel hose/pressure gauge attached so I can read it. This hose can be handed off, or they can grab either my main secondary (from my mouth) or octopus. I will then grab their vest, calm them (if necessary) with eye contact and "OK" signal, and then I'll calmly manuever them to the surface. I might even breath a little air into their BCD, but I'd probably wait until the surface. If they freak out - well, there are some ways of getting free and they are on their own without air - but, at least by the book, they'll be OK once they have air and are doing a controlled ascent with their buddy.
I do loan my sling to buddies, if they want it, when we are doing deep dives.
Please tell us under what situation would you hand a pony bottle off to a OOA buddy and not accompany them?