We love our Sodastream -- I absolutely hate toting bottles & cans from the store & then having to throw them away (actually the recycling bin, but it's the same trip). I prefer the models with the glass carafe rather than the plastic, which must be periodically replaced. I drink more water when it's carbonated. Chilling the water first helps with the carbonation.
We bought a second CO2 canister to use when the other is empty. We exchange it at Williams Sonoma for half the purchase price of a new canister.