In this thread, there’s info on how to save money on the cylinders.
I use my machine all the time. I wouldn’t drink bottled water otherwise because of the plastic waste, and I don’t ordinarily drink commercial soda. I make homemade sodas with fresh lemon juice/rind, ginger, mint, rosemary, etc. Also chocolate soda. That said, the sodastream brand diet root beer and diet orange syrups aren’t bad at all.