Halon is being phased out of the aircraft industries.
No new units being made, so stocks are being used up.
But there is a lot of stock. A 747 may have to have at least one unit change after a transatlantic flight. But as the suppression system has to be the same, they will fit another Halon unit. But new planes have different systems.
BAE are leading the development of thinner wall CO2 cylinders.
One idea they have looked at is Alloy Honeycomb cylinders. If that is a success then we could hope to see the same amount of CO2 as a 5Kg CO2 extinguishers is a unit not muck bigger that a traditional 2kg CO2.
A 2kg Co2 unit has 2kg of liquid CO2 stored in it, the rest of the weight, approx. 2kg is the weight of the cylinder and head. One reason steel bodies were phased out, the weight.
Weight is the main reason you see a lot of 6lt foams and 6kg Dry powder units, as they weigh in at approx. 9kg. This was chosen as it was deemed the "average" person can lift, carry and use a unit of that size.
There is a lot to be considered when installing a extinguisher.
When I had a fire around the back of my warehouse our big old 9L water extinguishers were far better than the newer 6L ones. Chubb reckoned the new ones were just as good as they have an additive and a spray nozzle. The additive didn't do anything and the spray wasn't as good as the jet.