Well if I've turned it on and maybe taken a test breath from it: I'm pretty confident it's working. On the other side, it's possible there's a second stage issue (octo) on your buddies system: not likely, but neither is a pony that worked when you got in randomly breaking.
You misunderstood what I'm saying - you take the reg your buddy is breathing from, ie their primary, not their octo. The primary is the one you both know is working
I dive a hog rig, so donating your primary is standard practice. However, even if your buddy is diving a standard rig, they can still donate the primary, so long as they're comfortable with it/know that's what you're going to do. Usually the person who is not OOA is the better one to go looking for an octo
Anyway, in my experience, in a 'genuine' OOA situation, people go for the primary regardless
T. I wonder if the pony use thing is somewhat geographical in nature. Not a lot, but a signifigant number, of divers up here use them. We often have poor vis. conditions and losing a buddy is, unfortunately, a fact of life.
It's possible - most of my diving is done in Asia. I personally only use a pony when doing deco diving (with a deco mix) or training. But if it's a deco dive then I'm using twins anyway, so I don't (shouldn't) need the pony for backup
But I myself can't recall seeing anyone using a pony for general rec. diving - not to say they don't, just that I haven't seen it myself
Maybe the OP should consider switching to doubles rather than getting a pony?