Thinking about moving to disposable paint cups but I'm not a shop and just wonder if the convenience is really worth the expense?

Absolutely !!!! I use all three sizes.
Gun clean up is a breeze, you'll save a bunch on thinner. I use aerosol gun cleaner now too, a big time saver and cleans the guns great.
Get yourself a 3M plastic primer gun too with the removable tips, practically zero cleanup.