My Air2 uses a different size disconnect fitting than do my auto-inflators or Prosub integrated octopus.
I tried my Air2 at 150-feet and it breathed almost as nice as my D-400 primary. For these people that say their Air2 like breathing through a straw, maybe they need to have it serviced. It's not supposed to breath like that. I switch off to the Air2 sometimes during a dive and have no problem swimming with it. I therfore cannot see why there should be a problem breathing off it while someone else borrows my primary for a trip to the surface.
I bought my inflator-hose-integrated ProSub octopus to add to an older fiirst stage that only had one extra LP port. The Prosub saved me from the expense, weight, complication, and unsightliness of adding an adapter to provide an extra outlet. The ProSub breathes OK, but not anywhere near as good as the Air2. The ProSub is, however, less expensive, more compact and uses a standard disconnect fitting.