I use this book in teaching, and am very grateful for it. However, there are a few "gotchas" that the reader/student should be aware of.
First, it's old. It was done in 1963 and won't be revised, since the author is dead. It thus has a very "traditionalistic" selection of texts, with philosophy more narrowly defined than I feel comfortable with. And of course, it doesn't include any of the textual discoveries since 1963, or any of the groundbreaking textual work, such as Graham's on the Chuang-tzu. There are major authenticity problems with some of the selections from the Kung-sun Lung-tzu and Tung Chung-shu as well.
Second, even for its time, it's conservative. The author was, to put it kindly, credulous about some early datings. The discussion of the Lao-tzu is particularly problematic. There is also an overly dismissive attitude towards the thought of some periods, such as the Han.
Third, it's somewhat biased, though in a very traditional way. The Neo-Confucian standpoint is more or less assumed true throughout. This detracts from the discussion of some documents earlier than the Neo-Confucians.
None of this is an argument not to use the book. But be just a bit careful if you do.