my understanding is this method can only be used for birds for your consumption, (or for emergency at commercial abbatoir eg if bird injured in lairage etc). For any birds to be sold, except in emergency as described, the stunning etc method have to be used and licensed people doing it in approved premisesI think.
but I may be wrong, not an expert, just what I read in the regs when looking at whether to keep our geese for meat as well as the eggs we currently keep them for.