Please do a search as over the last few years I and several others who have actually used both have made several posts on the pros and cons. These threads always devolve into a dog fight between the believers and non believers with most of the critics having never used one.
In truth, how well it "works" really depends on what you are trying to achieve in your entire conguration.
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I use an Air 2 on a lightweight travel rig as it allows me to use only 2 LP hoses with the reg (a Scubaopro Mk 17) placed on its side with all three hoses (2LP, 1HP) pointing straight down. This results in super clean hose routing. On this setup (and on all my others) I also use a 7' long hose which aides hose routing and makes air share a breeze.
The reality is that quite often in an actual OOA situaion involving recreational divers, the OOA diver will mug you for your primary. There is a really stupid thread on "primary take" that can safely be ignored as it bogs down in the semantics of training students to dontate the primary versus training them to have it taken, but in the end it makes sense to train students to dontate the primary reg so that when it is taken, they are not surprised and can adapt.
In that regard the Air 2 works well as divers HAVE to donate the primary and the Air is always easy to find as your hand goes to it numerous times on every dive. No one shoudl ever even vaugly consider trying to get a buddy to breathe off it - it was never intended to be used that way.
Originally, Scubapro used a separate pull dump on the right shoulder on their BC's so you coudl use the Air 2 separate from any dunmping function. However it is not hard to dumnp air through an Air 2 while breathing off it in either of two ways. First, if you have a pull dump on the corrogated hose, you just put the Air 2 in your mouth and then press out on the corrogated hose anywhere along its lenght. This lenghtens the hose and activates the pull dump via the cable in the hose. Very simple, and it does no restrict your head movements. You can also dump gas through the Air two just by pressing the large square deflate button. Since you use the buttons on every dive you learn which is which very quickly and pressing the wron one is a non issue.
There is a learning curve, but it is extremely short. Thse who say ascending while breathing off an Air 2 have most likely never done it, never practised it, and/or are essentitally ignoring 30 years of successful Air 2 use.
Since the Air 2 is used several times on every dive, it stays clean and I have neer encountered one as a tech that was full of silt, sand, etc, with a stuck exhaust valve or other issues that occur with a normal octo. The one thing I do see on them is a tendendcy for them to be poorly rinsed - some divers rinse the reg but ignore the Air 2. The good news is that the Air 2 tolerates this very well and with annual service this abuse poses no issues.
The Air 2 as it is often adjusted at the factory and by many techs breathes badly. But it uses the same basic internal design as the R390/R295 with only a slightly smaller lever and diaphragm, and when tuned for peak performance breaths quite well.
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On the other hand, a bungeed octo offers many of the same benefits. It is easy to find as it hangs blow your chin and that location keeps it out of the much. When combined with a 5' to 7' long hose, gas share is very easy. That approach also REQUIRES primary donation, and the long hose primary configuration is ideal for both the AIr 2 and bungeed octo.
In that regard, many of the opponents of the Air 2 oppose it in large part due to the "donate the primary" requirment and those same people will oppose the bungeed octo on the same grounds Just be clear that they are separate arguments.
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My advice is to consider where you are going with your diving. A long hose primary and bungeed octo is the norm for any techncal diving. If you will be strictly recreational and are going to take the time to configure a very lightweight rig with celan hose routing, then the Air 2 makes sense. If that is not a priority, then stay with a regular octo.
In either case, I recommend you consider a long hose and seriously consider adopting primary dontaion as your default air share method as those approaches work SOOOO much better.