Hi, here's my POV, sans actually owning or testing the "Aqua Air", compared to an "AirHawk" all air cushion.
I don't like gel cushions [too firm & no real-world butt conforming attributes] and would think the AA without added air would be
somewhat similar to a gel in as much as air compresses & and fluid does not. Apparently [unless I missed something], the AA is one big bladder and if you add air, as is possible, the water is going to slosh around when used on a bike.
The AH is strictly air and is
multi-chambered so as your weight shifts, as in a curve, the air chambers self adjust. There is a very slight delay as the air chambers self adjust, but is quickly acclimated to.
I carry my AH on long trips and don't use it unless my bum or lower back begin to anguish. I don't even strap it down to the seat, however, if you stand up on the pegs above 20 mph you could loose it.
In the past year or so I've been using the AH on my office chair. Since I can spend as much 16 hrs. in that chair coding software, the Air Hawk has come in very handy. My chair was comfortable in the beginning, but I would become terribly unable to work that long without it. A water bladder [nor a gel] wouldn't have faired as well or as long. IMHO
Maybe the AA single water bladder would be OK in the desk chair with added air, but on a bike I imagine you could feel the water sloshing around.
This is solely my perceived opinion of the "Aqua Air".
The "Air Hawk" cost runs about 20% more in comparison.
http://www.airhawk.net/ Available from many distributors.