Yup, all these kettles are water only as there is no way to clean the inside out.

The Thermette comes with a support ring that can sit on top of the chimney....this support ring supports a pot for soups etc so you can cook and boil at the same time. You do have to remove the pot to add sticks though so this is a good potential but not a perfect setup. How tall and ungainly it is etc remains to be seen.

The large Kelly can be had with an accessory kit....really a small two piece grill that sits on the firepan only. This way you can grill something or possibly support a tiny pot over the coals after your boil is finished.

I have seen someone make a hardware cloth "ring" that fits the Kelly chimney that could then support a mug or small pot, but this is a very tippy operation.

I then to think of these as hot water boilers exclusively.