> I found it cheaper and much, much more convenient

Cheaper? I don't see how. We're filling from the same CO2 cylinders, and my total hardware cost was less than that of a midrange SodaStream without the adapter you describe.

More convenient? Maybe, depending on environment and use.

But mine has advantages, too: More fizz, no counter space required, fewer fragile plastic parts, standard components that are easily serviced/replaced, and the ability to carbonate liquids other than water without worry of backspray gumming up a countertop machine's internal components. (Your unit's instructions probably tell you to use only water, for this reason.)

> you can leave the larger tank shut off and away from living areas so that a leak doesn't pose a hazard.

I close my cylinder's main valve when it's not in use, and the two additional valves downstream of it (at the regulator and ball lock fitting) also work, so I think a leak is very unlikely. Even if there was one, I would expect it to be noticed quickly or else too slow for the released CO2 to cause harm.

SodaStream carbonators are super common at all the thrift stores near me, so they're like $5 to $10. There's one on eBay right now for $25 with free shipping. The refill adapter was $10 on AliExpress, but the cheapest regulator alone cost more than my entire setup.