This book is a very mixed bag. To start with the negative, about a third of the text is made up of product placements for other vocal courses as well as mostly pointless gadgets and supplements. When I pay €30 for a book, I expect it to be free of advertisements. My second big complaint is that some of the explanations of vocal anatomy and acoustics are just plain wrong. The claim that the vocal folds "zip together" on high notes has been debunked for a long time, as has the belief that vibrations felt in the torso actually contribute to the vocal sound. And thirdly, I find Jaime Vendera's conversational tone, motivational babble, and awkward attempts at humour quite annoying.
On the upside, however, his vocal exercise suggestions are actually quite sensible. Slowly sliding back and forth between different pitches and timbres really is a very effective way of training coordination, and a much better starting point for practicing vocal technique than traditional scale exercises. So, basically, I recommend reading the chapter "Strengthening the Voice" and ignoring almost everything else.