I tend to avoid them if the shop is packed because I feel like people are getting frustrated with me if I take too long using the machine
But if its quiet then I use them because they're so fun, I like to try and scan the items as fast as possible
I find that the unexpected item in bagging area problem doesn't happen so much anymore, but I still find it annoying that I have to get an attendant to come over and confirm that I'm using my own bags.