The Air 2 issue is sort of a hot button. Some people like them and some people don't and in my experience, many who don't have not actually used one.
They are virtually maintenence free and will normally go 3-4 years before needing service. By virtue of their positioning and their constant use, they do stay much cleaner than a conventional octo and I have never had one get full of sand, grave, mud etc. They also tend to come into the shop much cleaner and in better general working condition than the average octo so there is a lot to be said for the underlying premise of the design.
Ideally, you should use your octo on every dive to ensure it works and to keep the crap flushed out of it. In practice, many divers never use the octo. I see several each season come through the shop that are basically non functional and would not deliver an adequate amount of air in an emergency. Some will have stuck exhaust valves and others will be full of all manner of debris and a few will be badly corroded in critical areas and have obviously never been rinsed. In this regard, the self cleaning nature of the Air 2 is a signifcant advantage, particularly when you conisder that statistically you will be the one trying to breath off the alternate air source, not your out of air buddy.
Some techs have problems with slight leaks after servicing Air 2's but this is generally the result of not replacing the small o-ring around the orifice. If you don't replace it, a very slight leak is nearly inevitable. Internally they are a very simple downstream 2nd stage design and use the soft seat as the R190.
With an Air 2 you do have to donate your primary, but that is good practice anyway especially if you are using a long hose. In 2 out of the 3 air sharing situations I have been in, I was mugged for my primary on 2 of them. So donating the primary is a more realistic way to plan anyway and in that situation, the Air 2 is always very easy to find and access which can be a key advantage.
With a more technical configuration using doubles and a backup second stage, there is no real reason to have an Air 2 and consequently many of the technical types tend to lead the charge in condemning the Air 2. But for more normal recreational single tank diving it does offer some advantages and is worth considering.
For solo diving with a pony and Air 2 is nearly ideal as it provides the capability of having a backup 2nd stage on the primary tank with out the problem of an octo getting in the way of or getting confused with the pony bottle's second stage.
The Air 2 is a very good balanced inflator and also works very well for inflating lift bags. In cold water it can be particularly valuable in that role as if it freezes up, it can be disconnected for a few seconds. Not something you can do with an octo or primary second stage.
In my opinion, the pros outweigh the cons and I think they can be a good addition depending on the type of dives you do and your configuration.
Given that I dive primarily doubles on deeper dives I no longer use an Air 2 as it requires a much longer corrogated inflator hose than I prefer to use with my BP/wing, but I still encounter situations where one would come in handy now and then.
Do some research, get several opinons and then make your own decision as to how it fits with your type of diving and configuration. You definitely do not want to decide one way or the other soley because of what an opinionated SB member said.
