I've read it and to be completely honest I wasn't impressed. Its central argument seems to be that if you eliminate animal products from your diet you will be healthier and will get thin. I have 20 kilos gained while being vegan that says otherwise! Rather than telling people to stop eating ice-cream and sweets they tell them to switch to soy alternatives. While soy ice-cream may be slightly better than dairy ice-cream in terms of calories and fat, it will still make you fat if you eat too much!
I read all their advice and everything they said was exactly what I was doing while gaining weight. Their ethical arguments towards veganism were much stronger than their weight-loss arguments, and I was incredibly dubious about their scientific arguments.
That said, it might work for some people. And knowledge is never wasted. I'd encourage people to read this book and weigh up the evidence. I'd encourage them to give it a go and see how it works for them. All I can say is that it wasn't a workable solution for me!