Bed Bath and Beyond does the $15 exchange, too.
I like it, because I live in a 550 ft2 condo - and it's a third floor walk-up. Between lugging heavy soda and finding a place to store it, the SodaStream won me over. Even though I know it possibly costs more, it's worth it to me. And the CO2 bottles fill about 60 liters, so a quarter a liter plus a little for flavoring isn't that bad.
It also keeps a bunch of cans and bottles out of land fills.
I don't get lost, I go on interesting side trips.