Most of this scanners v checkouts is becoming a moot point as time goes by.
more and more people are choosing to shop on line for delivery to their home at a tiem that suits them when they will be in which negates the need to go to do a big shop. This will increase and will reduce even further the need for checkout operators but their roles will now be as pickers in the store for the online shoppers so no real need for redundancies.
I think the self scanners are more intended for somebody nipping in for a few bits and pieces.
The picking for online orders isn't always done at the store, in some cases it comes from a purpose built warehouse elsewhere.