True, however the inflator and octo, in a combo unit
is in series. AKA inflator and octo coming from one hose vs 2 independent hoses. One could argue that they aren't independent because they come from the same tank, but that's missing the point. With the point being:
What is going to happen if your inflation hose has to be disconnected? You are going to lose your octo. This is an unsafe situation for your buddy...now he has no spare air source at all. You need to call the dive immediately. Simply losing your inflator, and your inflator alone, is not a potentially life threatening situation.
Of course everyone is entitled to their opinion as are you! I personally regard them as an unnecessary safety hazard. But, that's just me!
Well, maybe not just me but anyway.
If you are analyzing safety... which is safer, having an extra hose coming off the first stage or not?
Which is safer, having a normal octopus that is subject to a potential freeflow which has the possibility to completely drain ALL your air.. or using an air 2 which (should it start to freeflow) have the ability to instantly disconnect and stop the gas loss immediately?
You seem to think that should the air 2 begin to leak air, then the dive should be terminated because the hose would be disconnected and the diver would not have the ability to breath from it. However, should the diver wish to continue the dive, AND his buddy should need to receive air, then the pair can simply buddy breathe from one second stage. Apparently you feel this is a life threatening situation... this is not necessarily so. The fact that you think along those lines is probably related to being a new diver and the fact that buddy breathing is no longer being taught (as far as I know). However, it is a very useful skill and a viable option in openwater situations.
Your thinking on this topic also seems rather narrow in that you feel that should a standard BC inflator fail and need to be disconnected from the LP hose, that the dive could be continued (without the ability to power inflate) and this would (apparently) NOT be a life threatening situation.
Personally, I feel that neither orally inflating a BC nor buddy breathing are "life threatening" situations - assuming you have a particular skill set.
Another potential safety benefit of the AIR 2 is that it is much, much easier to disconnect quickly in an emergency. Disconnecting the normal inflator hose with thick gloves and in cold water with numb hands is NOT simple, easy or necessarily fast, Delaying the disconnection could result in an uncontrolled ascent which MAY be life threatening. Possibly as a new diver, you don't know this, but a stuck (auo inflating) inflator is a VERY common problem in comparison to other scuba gear failure modes. This type of failure is much, much more likely than a hose failing or even a diver running out of air.
So I am not trying to convince you that you should continue to dive after any gear failure, but on the other hand, possibly you have not considered some of these other factors.
I'm not selling air-2's either, I've used them for like 15 years maybe and have had very little trouble with them. I can understand why people don't like them, but they do have some advantages and your attempt to talk about serial and parallel failure modes is somewhat over simplified.
If you are going to try to analyze the safety of various systems, you need to understand the likelihood (and consequences) of each particular failure mode.
