Tried their self-scanning checkout. Gave up in despair as it is so slow.

They have this in the otherwise deeply civilised Sainsbury's in Canterbury. They also have someone whose sole job, so far as I can see, is to stand there ready to help anyone who is struggling with it. The scary thing is, there is clearly a need for that person to be there all the time. Which would personally tell me that it would be a lot quicker to have a quick-service till.