I also use self-checkout at Costco if I don’t have too much stuff. However, there are always two or three employees at work, checking membership cards and helping shoppers.
They get better through-put with self-check, but at what cost? Those employees could be running regular checkout, and save the cost of purchase and maintenance of the extra hardware.
I have mixed feelings.
I imagine, like everything else at Costco, there was significant “bean counting” done before they rolled them out across the enterprise.
I have always been impressed with Costco’s line management in their front end.