Went out and bought an iPhone 12 Pro to test. It does better than the 6 BUT my buddy was just lucky that day. I do get about 20% closer with the 12. It will come in handy mapping out new trails not yet on Google Earth. Using the Solocator app shows accuracy before the shot. Best for the 6 was +-16 feet and the 12 says 9 some of the time but almost always does 13 feet. The 12 is a lot faster. I am guessing it throws off fewer wild readings because it locks onto satellites faster. Solocator takes about 3 seconds to finish a picture and the iPhone 6 takes 3 or 4 times that long. So between faster satellite lock and knowing guessed at accuracy, I have had no wild readings with Solocator saying +-13 feet. Taking 2 shots of important points helps verify accuracy.
Now, fess up time: the U1 chip is likely not involved in any accuracy improvements. It is supposed to let you put an active tag (Tile) on something and get within a foot of it over a WiFi like range, say 150 feet. Tiles are $25+. Remember the the old shoe chips and the threat of a $35 "fine" if you did not return it?
The LIDAR function works and really gets close...at distances < 16 feet. Still, nothing you would use to mark a 2 x 4. Quite disappointed at how little the sales people knew about these functions.