I know you’re asking about syrups, but before you buy a Sodastream, have you looked into a DIY version? I made one of these a couple years ago. The tank holds way more CO2 than the ones Sodastream has. Not a proprietary tank is nice.
https://www.popsci.com/diy/article/2012-06/how-make-your-own-home-carbonation-system/
Edit: trying to make the link work.
I know you’re asking about syrups, but before you buy a Sodastream, have you looked into a DIY version? I made one of these a couple years ago. The tank holds way more CO2 than the ones Sodastream has. Not a proprietary tank is nice. https://www.popsci.com/diy/article/2012-06/how-make-your-own-home-carbonation-system/ Edit: trying to make the link work.