Always wondered if this would pass as a deal and decided to give it a go. I keep my empty sodastream canisters in the car.
Once a month when in need of a sodastream co2 refill, I use the nsw fuel app to find the cheapest coles/shell and go to fill up when almost empty (e10).
I buy a $1 coffee + the $19 sodastream refill and often use a 4cents/litre coupons from coles as well.
The $20 in-store purchase gets me 10cents of per litre of fuel. With a full tank from near empty between being between 50L-52L that's usually an approx saving of $5.
I get that it works with other items, however, most other items are overpriced/servo prices.
2 numbers: 7 and 11