SodaStream bottles are exchanged at Boots and other shops for full ones. At some point they changed the thread on them so an adapter for the Aeron adapter might be needed. It’s ages since I used my B96 with that fitting, I bought about eight full old type sodastream bottles off the bay but haven’t been using them .. just the odd plink with regular CO2 bulbs. The fire-extinguisher system is probably the optimal one, cheapest at least.