The Mustard Seed Garden Manuel of Painting had been a standard reference book for Chinese beginners of painting for a long time (though it ceased to be so quite a while ago). It remains a valuable summary of styles and methods in traditional Chinese paintings, and is of a lot of historical interests because it represents the scope and perspective of the authors some 300 years ago. It is really a fun book to read, but it would be dangerous to use the book as a guideline for appreciating traditional Chinese paintings cause this book was, after all, compiled with a very strict ideology of paintings, even ignoring and misinterpreting many art-historical facts.
I would have given the book a 10 if this was not a bad translation. First, we have to admit, it is an old translation. For whatever reasons which I suspect are related to the fact that the book was first published at 1956, there are simply many wrong translations in the English text. If you can read Chinese, I bet you would hardly resist the temptation of giving the book a thorough revision. I often laughed hurting my stomach when I read it. I will leave you to judge whether it's a good aspect or a bad one of this book.