Ah, that was why... About a month ago or so an old friend told me he wanted to get into spearing and I started window shopping for him and did see the One Air on fire sale. I have a 120 myself, so gave it a brief look over but then decided to recommend a Predathor Vuoto to him instead. He got one second hand back home for a steal.
The One Air is an interesting gun. It has so much mass compared to all the others and a few of us users have previously described it as feeling like a scalpel when you shoot it. I know it sounds weird, but it's just so easy to shoot, the trigger pull feels nice and the gun seems very accurate. But that said, while the demountable handle results in a very high grip much more in line with recoil forces than all the other traditional oleos, the handle is also what reduces the efficiency of the gun. To make it detachable, the barrel stops in front of the handle, in a bulkhead in the rear of the reservoir - as a result, the piston travel length is substantially shorter than on any other similarly sized Mares, Cressi, Seac, Salvi, etc.
I know people say that the Airbalete, which share the same internals and handle, is hard to aim but I would personally think it is the better gun - if it could be picked up for cheap. But again, it will have that short shooting barrel. That said, a Danish spearo had one in the 80cm size and he shot loads of sea trout with it and liked it.
The more I think about these guns, the more of a conundrum they become. It's a bit like one step forward and two back or some unfulfilled promises, at least. Perhaps, for a person who absolutely can not stand any recoil, this is a gun to consider.