Usually you will have a single staff member responsible for 4-10 checkouts to override the machine when your product doesn't register a weight, or you move items off the scale too quickly, and it wants them to check it.
It generally just works and is a lot quicker if you're just scanning a few items; surprised it hasn't really taken off in the US.
Most of the issues these days are when they introduce new features like less tolerance on the weight (sometimes adjusting already scanned items trips an error) or auto-scanning fruit and vegetables.