Ah yes, I've seen that brand for sale too. Auro and Ulla seem to be what our friendly and helpful local restoration paint specialist keeps in stock so that's probably what we'll use, but I'm quite interested in the other types of clay paint too.

ETA: Ahh, I think I see the deciding factor. The Finnish shop is referring to silicate-based mineral paints as clay paint - perhaps that's to do with the precise connotations of the Finnish term for clay - and the slaked lime ones all as chalk (or rather, they only have the one word that means "limestone", "lime", and "chalk").