They are incredibly simple to use if you follow the 3 instructions. But hey, people can't even signal when turning reliable, of course a lot of people are going to have problems with these machines.
As a former cashier I can certainly bag and scan efficiently. I actually like the machines because it reminds me - but they do get in the way. I'm maybe a quarter as efficient on them as I was on a proper register.
I assure you, I can reliably signal turn. I also assure you that any time an item fails to scan on the first swipe, it accuses me of being either an idiot, or a thief.