Aldi and Lidl - the discount supermarkets in the UK manage just fine with spurts without a self scan machine anywhere. They are constantly opening and closing checkouts as the people waiting varies. They seem to have a default to get staff off tills and back to the rest of the store when people waiting drops to some prescribed number.

Go in really early or late and there are no lines occupied until a customer waits - usually no more than a minute as they appear to have a strong focus on keeping an eye out.

I would say there's a shorter overall wait, and a far higher likelihood of getting out of the store in the shortest overall time than any of the alternatives at the competition.

So no, I haven't seen any of these much-touted speed benefits. Quite the opposite frequently.