The listing says 666 g or 2 kg. It does not say how many drinks or plates that is, which is the bit you care about.
Four things move the number, and anyone giving you one figure is making it up. What you are making — a stiff cream burns gas differently from a light foam or an infusion. The equipment and how it is set. Whether you run each charge all the way out. And how often the thing gets opened, because every reset costs you.
Better to measure your own place. See how long one unit lasts across a normal week, then read the sizes against that. A week out of a 666 g unit is comfortable. Two days out of one and you are paying in interruptions — go to 2 kg or 4.33 kg.
Same honest logic behind the 5 kg and 10 kg tanks. It is not about holding more for its own sake. It is about not stopping in the middle of a busy night to change something.
Whatever you go with, check it against the current manufacturer instructions for your regulator or siphon. Everything here is for lawful culinary and food-service use, inside the rules that apply.