Those are only situationally useful. They tend to be too dim and blurry, and if you’re wearing polarized sunglasses they can be totally black. Focusing on them long enough to make out what they’re displaying causes tunnel vision - you can’t really shift your focus from looking around out the windows and back to looking at the screen fast enough.
Back-up cameras are great for measuring the last couple inches of parking.
I don’t have that problem at all in my car.
I live on a one-lane road, and the turnaround in my driveway turns into foot-deep mud when it rains, so I back into my driveway. …About 300 yards of backing up, all in, with some fairly sharp turns and a steep drop on one side of my driveway. It’s really simple, as long as there’s any light; at night, the reverse lights aren’t really bright enough to see what I’m doing. BUT my display is about 8" wide; I’ve driven trucks and vans where it’s a 2" wide section on the rear view mirror, and those are a pain in the ass.