Let's start off with the very basics. Kotori and I and two other people in the WWCC are experimenting with HPA. For the most part, using a 48 cu-in HPA tank is a drop-in replacement for a 20-oz CO2 bottle. It's a bit larger diameter but the length and weight is the same and the equipment is the same. The tanks have a built-in regulator that takes the pressure down from 3000psi to 800psi. You can then use your regular CO2 regulator with it. Because there is no phase change, it is practically impossible to freeze up. Just as an example, the stern gun of my VU freezes up my CO2 tank and regulator after 4-6 shots. At the recent battle I was firing almost continuously as shown in the video and the bottle barely cooled off. The fill station is also simpler: simply connect it to the fill station, open the fill tank and let it equalize, close the fill tank, release pressure from fill valve, and disconnect. it can be done in less than 30 seconds. There is no need to drain the bottle before refilling it, so less gas is wasted. Also, most tanks have a pressure gauge on them that shows how much pressure is left and you can decide to fill up or not. The fill stations use scuba tanks, which can apparently be filled more cheaply than a CO2 tank, and are also more common. Divers can use their old tanks if they have the right valve. I was also able to rent a fill station from a PB store for around $15.
There are a few safety concerns that must be addressed. First off, there are two types of bottles: aluminum and carbon-fiber composite. DO NOT EVER USE THE COMPOSITE BOTTLES! They degrade when exposed to moisture and we will be doing a little bit more than simply exposing them. Second, word from NABGO is that Steven of Strike Models was sunk and the pressure gauge on his tank didn't like the water. I'm still looking into this, so I'm not sure if it is an issue or not.
There are a couple non-safety concerns that we are still investigating. The fill station is much simpler to use, but we don't know how long it will last. We are still investigating the endurance of the fill station. The second consideration is that there are tanks equivalent to a 20oz and a 3.5oz CO2 bottle, but nothing in between. We are still looking for something suitable for cruisers and small battleships.
Overall, they look very promising, but we are still exploring some of the issues. The big no-no so far is that composite tanks do not take to water at all and must be entirely avoided.