I am not altogether surprised. Unfortunately, our Search function here on SB is not as 'robust' as we might prefer.
The majority of threads on the subject are posted in this subforum - Tanks, Valves and Bands - as well as in the 'Solo Divers' subforum.
Try this: type 'pony bottle' into the Search bar (without the quotation marks). If a menu pops up with check boxes such as 'Search titles only', or 'Posted by Member', or 'Newer Than' or 'Search this thread only' or 'Search this forum only', make sure you uncheck ALL of them. That way you don't restrict the search to any particular member, or forum.
You should get a list of ~101 posts to look at, in a variety of threads.
For bettter or worse, the discussion in this thread veered off a bit, in the direction of how to use (or how NOT to use) a pony bottle, rather than addressing your question, about what equipment options are available, and why one might be better or worse than another.
That is both the good and bad of a social media forum like SB. You get mnore than you were expecting, whether it is always what you want or not. 
