Most dive teams including ours use the AGA. We also have 4 Kirby Morgan hardhats for situations also. The AGA is great with wired comm units as we use the wire both as a tether to our tenders and can use them for sledding in the river here in Michigan
The AGA breaths great and we have yet to have a free flow or catastrophic failure that could endanger our divers. They have a double seal and seal easily over latex hoods. If used properly in hazmat environments, they will not leak in foul water or smell. The OTS Guardian on the other hand does not seem to work well with wired comms, (maybe it's our fault) and a hard breathing (also could be our fault). The AGA also allows us to run of surface supply air from either a bank of tanks or compressor using the same umbilical as the Kirby Morgan hardhats. Deep dives it allows tenders to change gases without the diver worrying about them (to an extent). The AGA unlike the Guardian cannot have it's mouthpiece removed for storage or tinkering with the breathing balance to increase or decrease demand.
The down side to the AGA is unit cost, increasingly fragile communication lines, left side hose that goes around the back of our necks. We can never seem to keep the face visor clean or free of scratches. And as mentioned above cannot balance the breathing without a tec tinkering with it. Also due to the AGA being positive pressure, many will find out that they use a little bit more air than the Guardian.
Detroit and Grand Rapids had the Ocean and Ocean Reef and for some reason or another, auctioned them off and bought brand new AGA's and KB hardhats.
