Interesting, but sometimes I have a hard time believing someone that is trying to sell you something. At least they aren't trying to sell you a specific brand of food or anything. Seems to be an interesting ebook, but there's plenty of free Yorkie health guides out there.
There's pros and cons to each argument, but if you have time, making some food for your Yorkie really isn't that time consuming. We've been giving Yoda a full chicken drumstick at dinner time. All we do is put the drumstick in boiling water for 10-15 minutes, and cook it like that (nothing added). Take the chicken out, let it cool, take off the skin, and cut into tiny pieces and mix into his Royal Canin dry food. He really likes chicken!