Rescue 1.
You are correct in assuming that you press the two sides to release the catch (twice
). This piece of kit is favoured by the US Coast Guard and presumably it's a matter of risk management i.e ratio of people falling out of the helicopter versus helicopters going in the drink. We used it for crew safety in SAR type ops as much as photography over the 10 years or so.
It does work well and releases very easily with the added safety of the second release. For underwater egress, I always suppose that once you have your reference point and good training, reaching to your waist to release two catches is just as easy as one; however we know that pressure bursts pipes as we say, so maybe a bit of added stress at the wrong time might not be favoured, particularly by those hanging upside down without any underwater egress training at all.