Finally got a workflow for home beverage carbonation that's affordable and without paying Sodastream (subject to BDS) or anyone else for overpriced proprietary cylinder refills. 🎉
Walked into the local Roberts Oxygen to ask if they could refill before buying a proper cylinder, and walked out with a 5lb (2.3 kg) one for $109 including tax, swappable for $20 when it runs out.