And of those, how many does this help, and how much? Like does this mean I could look at a map application while my wife drives for a few minutes and be ok? Or does it help a lot of people be able to read for a long time?

In my family, Apple's implementation helps only a small amount if at all. I'd also love to see some real statistics. What I think is really missing is coverage of peripheral vision, so maybe a similar feature built into AR glasses could be a real solution.