Regulators - Octopuses
A "same-source" octopus is an extra second-stage regulator that attaches to the same first stage and air supply as your main regulator. Your own same-source octopus is only useful to your buddy, and then only if you are together. The only same-source octopus that will be of any use to you in an emergency will be your buddy's, not your own, and again, only if you are together. In the tropics, where you can see your buddy 100 ft across the reef and the likelihood of getting separated is slim, this scheme can work very well.
However, in the low visibility conditions of the North Atlantic, counting on your buddy to be there with your emergency backup air supply when you really need it is courting disaster. You can not and should not rely on any air source that is not on your own back.
The same-source octopus is merely an economy measure that avoids the expense of an extra first stage and tank, at the price of reducing the safety benefits of the device to near nil in many circumstances. If anything, a same-source octopus may actually increase your own personal risk by doubling the chance of a second-stage regulator failure or free-flow. For true safety, you should carry a separate independent air source, such as a pony bottle or second tank and regulator, so that it will be of use to both your buddy and more importantly, to yourself.
One design that at least minimizes some of the handling problems of the conventional octopus is the integrated BC inflator. Not only is the combined inflator/regulator always handy when you need it, but when it inevitably free-flows, you can simply pop off the quick connect on the air hose. Then reconnect the hose, and hopefully, it will work again. If not, just leave it disconnected, and use the oral inflator, or your drysuit inflator if you are using one.
If you ever actually have to use one of these to share air, remember to give away your main regulator, and breathe off the octo yourself, since it has a much shorter hose. Chances are, by this point your "buddy" has already snatched your main regulator away anyway. A drawback of the integrated designs is that they all seem to use non-standard quick-release hose connectors. This means that your inflator hose will only fit your inflator, or one just like it. The usual reason given for this is that the standard connector doesn't flow enough to breathe from. Sounds like BS to me, but there's nothing you can do about it.
