Thanks Travis,
I agree with you, Cartridges are pretty inexpensive when bought in large quantities; my greatest fear was that the siphon required a "minimum level of ingredients", buying the 1L model and that one of two things would happen: (i) that I scaled down the recipe and for it to not work properly or (ii) not scaling it down and wasting ingredients.
I've been searching the internet for a while and, though I haven't found a direct answer, this doesn't seem to be a problem. In all of the recipes that I found that made any reference to using a bigger sized siphon (including some from modernist cuisine) it just said to increase the amount of gas. This may be only true for those specific recipes but I haven't found any saying you should increase the amount of ingredients, and there is talk of maximum level but none of a minimum level.
The biggest drawback if the batches is when you are doing a recipe in which you need to let it sit in the siphon for a long time.
I ended up ordering the 1L model. Hopefully it'll work fine (I'm confident it will).
Best,