Boots used to ( I don't know if they still do?) sell these in the 1990s. As I understood it then, and as I understand it now, they are primarily for marinating and slow cooking stuff in (like any other unglazed earthenware pot which absorbs flavours into the ceramic walls). They are not intended to replicate a tandoor.
However, if you wrapped it up in firewool and put charcoal (and an air vent) in the bottom.....?