The book, Humming Your Way to Happiness, is actually supposed to be about harmonic toning/chanting. I guess the publisher thought this title would have more appeal, which sort of shows you how much confidence they had in the book. The subtitle is "An introduction to Tuva and Overtone singing from around the world."
There is some interesting information in the book, and I'm not sorry I bought it (I guess), but to me it reads like a school term paper. It appears that someone who does not actually know how to do harmonic singing did some research and mashed it all into a very short book.
A clue to me was that the author referred to Tuvans, the residents of the country Tuva, as "Tuvinians." Uh-oh. I've been a Tuvaphile ever since the book, Tuva or Bust, was published (late 1980s, I think). I've got several CDs of Tuvan music and have read various books on various cultural topics that mention Tuvans. I've never heard them called "Tuvinians."
There are a few pages that describe how to do throat-singing, but...throat-singing is not an activity you can do without hearing it. And there's no CD with this book.
So, if you have bought and worked with the Harmonic Overtones book and CDs, have watched the Ghengis Blues DVD, have worn out your Hun Huur Tu and David Hykes CDs, and you are still craving more info on the history of throat-singing, you may well want to buy Humming Your Way to Happiness. Otherwise, I don't recommend it.