The DGX Gears XTRA first stage offers an extra choice of either a typical standard 300 Bar DIN inlet fitting or a special DIN fitting that includes an auto-closure function. Our service technicians tell us one of the most common reasons for needing an overhaul on a first stage and/or SPG failure is contamination introduced while handing and rinsing the regulator after diving. The auto-closure feature (aka ACD) on the first stage shuts the DIN inlet when not fully engaged on the valve, potentially avoiding the inadvertent introduction of water and other contamination into the first stage. Although the auto-closure feature is popular it is also controversial, some divers who are meticulous with their equipment care feel the auto-closure feature just introduces another potential failure point (causing no breathing gas at all) and prefer the standard 300 Bar DIN inlet fitting. We do not recommend the ACD option for use in technical diving applications, especially where the diver may perform valve shutdown drills. The XTRA gives you the choice of with or without auto-closure, the price is the same either way.