After reading this entire thread through again it appears that perceptions of the "One Air" have been very much influenced by a lack of early information, at least in English, to explain its idiosyncrasies and what have then been deemed to be failings. I now think that the muzzle on Broseidon's gun just bore marks because that is the only way to tighten the muzzle up, there are no muzzle ports to key into with a C-spanner or a rod passed through the ports, so the jaws of the spanner have to bear on those flats in the muzzle sides instead. No doubt the marks can be avoided by using the right sized tool which is a snug fit, but in that particular case someone may have just used an adjustable jaw spanner on it and the jaws rocked slightly on the flats marking the anodizing.
The problematic line release behaviour will be dictated by the mechanism elements located inside the removable rear grip, a look inside there should explain everything. They are outside the pressurized section and it should be possible to simulate the problem by just playing around with the detached rear handle. If the line release lever swung fully forwards stops the sliding pin in the grip section that pushes on the opposite pin sticking out of the rear of the pressurized section from fully retracting then that is where the "problem" lies, especially if there are no biasing springs in the rear grip housing to reverse the action without you pulling the line release lever back manually. If the line release lever was heavy enough then it should fall back on its own with the muzzle raised to cock the gun, but it appears that it is not, so you have to push it back with your fingers. Straight after the shot would be a good time to do it.
It now seems to me that the "One-Air" side tanks are mainly there to add some inertial mass due to the extra metal in the side tanks' curved exterior walls (for recoil reduction) and increased water displacement (floatation) to offset that extra weight in order to maintain post-discharge gun buoyancy. On pressurized tank capacity alone the gun is going to be the same as any other 40 mm OD (about 38 mm ID) tank on a pneumatic gun, so except for any additional friction reduction in the piston used the real benefit is in the vacuum muzzle equipped inner barrel. The downside of this design is the extra bulk of the tank for swinging the gun around in terms of it being a bit more of a paddle and the gun being somewhat longer, given its piston's powered travel distance, with some of the trigger mechanism now sitting rearwards of the pressure tank rather than inside it, as is also the situation with the "Airbalete".
When I first heard of the "One Air" gun I thought that it was all about having a larger capacity pressure reservoir, which seemed a bit odd as you usually have a larger reservoir for high pressure shooting to keep the gun's compression ratio low, but a vacuum barrel means a lower start or initial charge pressure can be used, so why try for a low compression ratio by having a big tank? Well the answer is that it does not have a bigger tank, at least in terms of a pressurized tank, than any of its competitors. The curious thing is if you aim to increase the inertial mass, then why shoot only 6.75 mm OD spears and only have a 11.2 mm ID inner barrel? You don't really need the extra gun mass as you are not shooting heavy spears where recoil could be a problem.
The above comment isn't meant to be a criticism, it is just trying to find some rationale in the design, above producing a different looking gun, which it certainly is. The answer may be the bigger inner barrel gun is yet to come, the "One Air" being the first edition to try everything out after the "Airbalete" proved the removeable handle.
Maybe the "One-Air II" will be a future version, or should that be the "One Air 13", which will shoot larger diameter spear shafts.
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