Air2s are heavy, and have to be long, so they really hang down below the diver. These are two of the reasons why they aren't used in DIR setups. They also use a proprietary LP inflator hose fitting, which means you can't swap out hoses with teammates' spares, or borrow somebody else's wing to put on your reg, unless you change the hose. Standardization of equipment, and the ability to share spares, is part of the DIR approach to diving.