I read all the above posts, agreed with most, and was ready to add my comments - but
Mtracer beat me to it. I had the exact same experience. I used to think electronic shifting a gimmick - and probably for guys who couldn't tune their mech detailers. Recent Ultegra mech systems (6800, 8000) shift like butter and are incredibly durable. But after getting used to 12 spd Di2 then spending a day on my gravel bike (GRX/Ultegra), I kinda laughed at myself. Yep, I'm spoiled. I absolutely love Shimano's Di2. Not going back.