In practice we have found it to make more like 45-50 litres, depending on how bubbly you like it.
Presumably the “60L” figure is for people who make their bubbles just above flat.
The canisters we use have a higher safety rating as they are made out of stronger materials. As such, they can be filled with 450 grams of CO2 perfectly safely, so you’ll actually get an extra five or so litres out of your beautiful Bubble canister. For the same price as a Sodastream branded one. And it’s delivered.