I used the UK ETA app and have had zero issues. When checking in with DL, I noticed the verbiage on the boarding pass was slightly different -- "INTL - VERIFY PASSPORT AND VISA" or something to that effect. In the Sky Club, the agent couldn't do a BP reprint without swiping my passport again, but no issues at the border. The e-Gates worked the same as they always have. I barely stopped walking between the plane and the revivals lounge. It's a great time to visit the UK without the crowds.