Demonform is quite inhuman. Fluff-wise, it would not be unreasonable to be, for example, a collection of gleaming steel limbs orbiting a dazzling diamond core, with a glowing, radar-encrusted spun-copper head hovering above.
But I am unsure as to what extent this frees demons from human needs.
Do they need to eat, drink, or sleep?
Can they catch diseases? Or be poisoned?
Obviously, under most circumstances a un-covered demon is going to be under a lot of heat from the God Machine long before starvation or even dying of thirst is a real issue, but I can imagine scenarios where a burned demon might survive days — enough time that thirst could become a real issue. Would it?