Hi Damein, some very good points there.
The question of whether recreational dive boats/operations are setup to allow or accommodate rebreather divers. That landscape is under going a considerable amount of change. I can still reminder when nitrox was new, and most charters when highly resistant to anyone exciding air profiles even when you were on 36%.
My own experience with rebreathers (both SCR and CCR) began in 1999, so of have seen a quite a transformation here in the US and the Caribbean go from “WTF is that!” to operations being moderately comfortable with the idea of seeing them on their deck. Often times the key is not the equipment you are using, it’s the diver using it. Some of the boats I routinely dive with in Florida know well enough to extend certain liberties’ like exiting the water 10 to 15 minutes later than the OC divers to the privileged of jumping in 15-20 minutes ahead of everyone for the second dive to do my own thing.
Enough said there. With the GEM, the initial purpose of this semi-closed rebreather is as a gas extension device, so that for example a diver with truly lousy air consumption rate could last as long as a diver with a very low air consumption rate with needing to use larger tanks that diver. For me, a single 80 cuft tank with 36% is enough for completing three one hour dives in 60 feet of water. So for a typical two tank boat dive, one tank is all I need – less weight, less space on the boat.
From a U/Wphotography stand point, the real benefit is reduced noise. While a SCR is not as quite as a full CCR, the reduction in noise generated by bubble exhaust compared to OC (and I don’t care good you are at holding your breath for a shot) is quite significant on influencing the behavior of the subjects you are trying to get images of.
“Given the travel limitations for pre-packed cartridges, hassle of setup and travel weight, I tend to think I'd opt to use twins or sling an 80cf cylinder for extended dive duration before running something like a gem.”
Really? I am done with those days of diving twins. The first to thank me was my back. Second, the limitations of traveling with a GEM are about to get even easier. The unit itself is as compact as any SCR or CCR currently on the market can get. And the choice of using or not using pre-packed scrubbers like the Poseidon requires or the Micropore cartridges the GEM uses are about change as KISS is coming out with a repackage GEM scrubber that uses the same sorb as most other CCRs. Something to think about.