Years ago I read an article about the proper way to adjust a car's side mirrors. Most people don't do it right.
I used to adjust it that alternative way years, or possibly decades ago. I found that it made it harder overall and eventually gave up, because I realized that although I could see the blind spot, I just ended up leaning my head to the left to see down the lane. I figured that I would be better off leaning slightly to the right to see the blind spot in the mirror.
Also, that adjustment is illegal in California. The vehicle code says that the side mirror must be adjusted so I can see 200 feet down the lane. I doubt that I would get a ticket though.
As for the Model 3, yes, it takes getting used to checking the screen first, and then when you are ready to go, checking the mirror. After a lifetime of doing the opposite, it's a hard habit to break. But it does work a lot better than the ultrasonic sensors in my older Model S, which I wouldn't rely on to react fast enough. And you can get used to it. But I wish that Tesla had put a more conventional blind spot indicator in the mirror.
I understand why they didn't do it in the original Model S, but with later models, it was more "we do it this way" than it's what customers want.