I first heard about this book when researching homeschooling curriculum. It was heavily used in My Father's World. I never actually used that curriculum, but I still collect books from it when I find them in the wild.
This is a good overview of people groups around the world, if it is a bit dated. I considered looking up groups as I went, to see what's changed in the 20+ years since this was published, but decided against it. It will be a good reference book if my youngest needs to write a report about one of the cultures mentioned.
I was surprised how diverse the book is. For example, Turkey has three sections devoted to people who live there. Several other countries have 2 or more sections about them. I found that refreshing.
I read it cover to cover, but I'd recommend someone use it in their devotion time, praying for groups as the Lord leads, or for research purposes. It's a lot to read straight through.