I bought a Soda stream last year. I really don't like flat tap water. I get bored with it all too easy.
I was starting a diet and wanted to reduce my tea and fizzy drink consumption.
I don't like any "Diet" versions of fizzy drinks, so they had to go.
I was worried it would be a fad and soon it would be back in the cupboard.
Totally the opposite occurred. I found i like plain soda water cooled from the fridge, It worked great with my morning runs, taking a litre bottle with me. (for after the runs)
I then found i enjoyed sitting at the computer with a half litre bottle, sipping as required. My water input went up and other drinks right down.
Now and again i put a bit of cordial like Vimto in.
Getting the gas swapped is easy at Argos, so i think that is the reason it is still used daily.