I'm glad you're getting good info. There are some people that will tell you there is only one way to do things, and that may be true if you're going to consider yourself a certain type of certified diver. There is nothing wrong with that for them but it may not be for you. The tech world has come up with allot of good ideas that can be translated to recreational diving, others don't do so well. Do you really need an 6 or 8 foot secondary hose for a shallow water dive in Cozumel?
Remember every style you dive has trade offs, all of them. Your diving style might make a large pony bottle both unnecessary and cumbersome ie shallow beach dive and kayak diving. If you dive to depths greater than 80' (for me anyway) you probably need something bigger than a 19cf bottle.
I would suggest that you take your pony to an easy site and breath it down at depth. See how long it lasts. Refill and do an accent using it. Same for a horizontal swim. Get very familiar with the properties of the tank under water and that may help you decide how or even if you want to continue using it.
When you decide how you want to mount or sling the bottle, use it in a controlled environment to get very comfortable with it's limitations. When an emergency happens the stress level goes up and things that aren't second nature can become stressful to the point of failure. I've heard stories of people diving with pony bottles that never even tried to use them when they ran out of air.
Last but most importantly, have fun trying this. Playing with new gear is always fun!
Good diving.
