Good write-up, but I’m not sure if I agree on your Starbucks example.
akin
132

This is a good comment and I agree with you. They might have been better off putting a “PAY” button right beside the bar with action buttons on it. Off to the right and possibly a different colour to differentiate it.

I particularly enjoy your use of “clever”, which is probably the best way to say that a function is not visible at all. “Clever” should be the last thing you want in a design.

Thanks for the feedback