Supermarket self-checkouts. Good, bad, indifferent, nightmare ?

Awful. The ones in my nearest store will not recognise my bag. So I have to transfer all the items from my basket into a pile before repacking them in my bag. At least two items per shop will not be recognised, so the attendant has to come to over-rule the computer. Only two tills are staffed and they have enormous queues from everyone wanting to avoid self service.