A pony bottle, is not intended to solve skills problems. They can however, do that by the simply being available when you need it; in that case, usually due to diver error. A pony bottle, is NEVER included in one's dive planning.
A rec diver, does not always have to dive with a buddy; it's called Solo or Self Reliant certification. A self reliant dive buddy, makes the best buddy. I have been slinging a pony bottle, since my 1st dive as a cert OW diver. I even slung it during my AOW course. 1st pony was a 13cu Catalina; sellers regret for selling it when I got a 30cu Catalina I know, when I am at 130', my 30cu pony, when full, will bring me safely to the surface. I also knew, my 13cu pony, if I was below 60', would get me to a buddy, not the surface. Either way, it was only to be used, during a primary gear failure, and never used to extend a dive.