Personally, I don’t think the technology is a failure. It’s the implementation that’s the pain point.
I’m no fan of Walmart, but the local store has the lenient self checkout machines that don’t make you place and leave your items in the bagging area. And there’s a hand scanner for each machine. The hand scanner is pretty close to instant, so I can literally scan an entire cart full of items in under a minute (with caveats) and you don’t even have to take things out of the cart to scan them (with caveats). Sometimes there are hiccups and obviously some items are sold by weight, so that’ll slow things down.
But even with all that, the implementation is the pain point because they’ll only have 1 person running the machines, so if they have to run off to help a customer or multiple people need help at the same time, you just have to wait. Also, the particular store I go to shuts down half the machines ridiculously early in the evening. When the machines break, they stay broken for weeks or months. And they have some kind of ridiculous system where some of the machines are cash-only, some are card-only, but the majority will accept either – this adds to a lot of inefficiency because a lot of customers don’t know which machines are which and if you mess up and pick the wrong one then things get tied up while you wait for a cashier to come and transfer you over to a different one so you can pay.
The other big factor is that customers were trained on the old shitty style self checkouts where you had to scan each item one at a time, place it in the bagging area, leave it there until you pay, and if so much as a speck of dust landed in the bagging area or a piece of onion skin fell off, it would freeze up. So even with the new lenient hand scanners, people still do it the old and slow way.