The whole "being green" thing has contributed a lot to their recent success. Also their flavors (afaik) use actual sugar instead of HFCS and diet flavors have no aspartame. I use mine just to make soda water and love it.
For comparison, considering only the cost of obtaining carbonated water, and assuming water is free (since it isn't a significant cost), in New Zealand dollars:
1 L of store bought carbonated water: ~$0.99
1 L of water at the lowest Sodastream carbonation: $0.20
(assuming $12 / 450g of CO2, 450g makes 60L).
1 L of water using market rate food grade CO2: $0.0032
(assuming a 3.5 kg cylinder makes 467 L and costs $15
to fill).This article provides information on the DIY approach: http://m.popsci.com/diy/article/2012-06/how-make-your-own-ho...
Sure it might be cheaper to go food grade and do it that way, but I am more than happy saving even a smaller amount of money, because it adds up quick.
There are quite a few people I know personally that drink it as well (non-Europeans), mainly because it is better for them than regular soda.
Some eco-friendly system places here in Copenhagen now have their own water filtration system and make higher-quality still and fizzy water on site.
Who's disposing of those things, they are much cheaper to swap out.