I wrote the following during a particularly contentious pony bottle discussion on another board about 12 years ago and subsequently posted it here about 9 years ago during a similar discussion. Some of it is a comparison between tech diving and rec diving and not all of it is applicable to this thread but much of it is.
"At this point I would like to state that I wholeheartedly agree that when it comes to technical diving then the Team Approach is the only safe way. In those dives any problems have to be solved at depth and unless you have an integrated team who have worked and trained together there can be disastrous results. Ideally we would like to have the same situation in recreational diving but that is frankly being unrealistic. Let's compare the two groups. Most divers who go on to technical diving are addicted to diving in one way or another. They eat, sleep and live diving, spend the money on equipment and training and also spend a considerable amount of their spare time diving and developing their skills. Most recreational divers get certified and maybe take an extra few courses so they can dive when they are away on vacation and maybe also do a little bit of local diving during the summer. They are not part of a Diving Team and even if they have a regular buddy it is still not Team Diving as GUE would define. Unlike the Technical Divers they do not go away on Dive Team trips but go on vacation with their families where they may take a charter or two to get in some diving. I am not sure how many dives a year would be average for this group but it is probably less than 20.
So what happens when members of this group raise the issue of ponys as a redundant air source. Normally a member of the technical diving community will advise them not to substitute equipment for skill, or some such statement, and tell them that you should rely on your buddy for your redundant air source. This is often the same individual who on a different thread is lamenting the present quality of training and the poor diving and buddy skills that recreational divers exhibit. That's right, although he does not 'think they are safe at any depth, he is quite prepared to tell you to trust those same divers with your life. When you point this out you are advised that you should only dive with buddies that you can rely on. This is sound advice but it is not always practical if you want to take a day charter while on vacation or if you are even going with your local club where there may be some newer divers with limited experience. Yes the technical divers will travel with their team, diving after all is often the reason and almost the entire focus of the trip.
So as a recreational diver on vacation you can, well! what can you do if you listen to this advice? probably play golf. If on the other hand you would like to dive and have a concern that you may be faced with a situation of diving with an unknown buddy whose skill set and response in an emergency are also unknown then you may want to make yourself a little more self-sufficient when it comes to the one thing we really need when diving which is air. Oh no! protest the pony detractors, look at all the complexity and task loading you are adding to your dive, you are diving an unbalanced rig, think of the extra weight swing from the extra air etc. These the same divers that regularly have 4 different regulators some delivering gas that could kill them if used at the improper depth. No they say, you are adding too much complexity, what if the gas you have in your pony is not suitable for the depth you are at. It's a pony tank guys, we fill them with air, yes that stuff you use for tires, believe it or not it is not toxic and can support life at all recreational depths. It will take someone about 2 minute to learn to how to deploy a side slung pony and probably less than 30 seconds to actually do it even under duress. Guys, to suggest that most recreational divers do not somehow have the capacity to do this is frankly insulting. Oh yes, there are a few that may not have the competence to do this and other things, these are the guys we are trying to protect ourselves from when we get inadvertently buddied up with them
OK now that you have your pony these same guys are going to look down their noses and suggest you are obviously incapable of gas management and are a dangerous diver because now you have the pony you obviously are going to use that emergency gas to extend your dive or push the limits etc. etc., after all if you knew what you were doing you would do it their way because doing it any other way is wrong. I do not know how many divers there are but I am confident that these same Technical Divers do not represent ten percent of the diving community and it is probably closer to one percent than the ten. Their ideas, methods and discipline are critical in the diving they are doing but it does not mean that recreational divers need to follow these very same methods. You may not want to tell them that though because they do sometimes get a little upset.
Well I have talked about a common reason to have a pony for those times that you are diving with an unknown buddy on a vacation for example. Why else might they be a good idea. Why might I want one when I am diving with my regular buddy who has always been reliable and stayed close. An example might be that your reliable buddy who you have practiced emergency drills with turns out to be an absolute hoover when the sh!t hits the fan and what would normally be an adequate reserve is diminished quickly. Much better to have the extra gas than be forced into a hurried ascent. Another consideration in our lakes diving is that freeflows are not unknown and for some people are quite common. If the conditions are conducive to freeflows you may just tip your buddies reg over the brink when both of you breathe from it, a redundant air supply can avoid this."
