I generally like them, but as others have said there needs to be a limit on the number of items you have. There just isn’t enough room to bag all of the stuff if you have more than about 20 things. Second, you should have to earn the right to use them. They should require using a shopper’s card to use them and include whether you’ve proven yourself smart enough to use them.
“I’m sorry, sir, but our records show that you aren’t equipped to handle the rigors of the self-check process. The line for a cashier is to the left”