s'cuse meh - I mistook that query for your signature line.
The big cylinder is for initial inflation onshore - it looks a bit Heath Robinson but actually inflates up to the 11psi max without leaks. It means that I can fill the boat without hunching over or moving the kit about too much. The fact that it cost me exactly nothing was a big plus
It will fill the boat to working pressure about four times.
The little one is the onboard kit and connects to the gauge and adaptor carried in the Pelicase. It holds about 90 litres and it's fine for topping off the tubes or airdeck if required. In the event of a total deflation, I would need to blow the section like a balloon before adding the final pressure. That's a 0.4L cylinder and the associated fitting is from an old BCD.
TBH, if the boat was bigger and had a hard deck, I'd just pack a pump....