1. If you don't have an airfryer you can also bake the meatballs in a regular oven. Preheat the oven to 220 degrees C and bake for 17-18 mins or till done. The baking time will vary depending on the type/size of the oven so keep a watch. The meatballs should be light golden in colour.
2. Since onions tend to release water it is ideal to make the meatballs and airfry/bake (basically cook them) before freezing. Do not freeze the uncooked mixture as the onions will turn soggy (and smelly) upon thawing. Cooked meatballs will last a long time when stored in an airtight, freezer safe container. Just remove as many as you require and pop them in the microwave before serving (or cooking in a curry)
3. We have had best results with the Brazilian beef available at Carrefour (tried it twice) and a bad experience with veal (avoid it if possible)