The three (not quite redeeming) strengths of this book are its reasonable price, readability, and great example essays for each genre of writing discussed - some essays by professional writers and some by first-year college writing students. The example essays represent a broad range of styles and voices, allowing students to see the variety of "right ways" that a person might write in a particular genre.
As a teacher, however, I feel books such as this are something of a waste of time for my students. The only way a person can truly improve at writing is to write, not sit around and read about writing. Aside from the example essays, the reading itself is terribly dry, and I would in fact prefer that my students spent their time reading socially relevant and thought-provoking texts and freewriting on them instead of reading this text. Most basic writing-process guidelines that a freshman comp student will ever use (if he or she hasn't already learned them in high school) can be found in more multipurpose texts such as Diana Hacker's _Writer's Reference_. The number of items I assign my students to read in this book each semester is not even worth their buying it in the first place.
If you are considering this book, I urge you to look over the much denser and more helpful _A Writer's Reference_ instead and save your students the money for this field guide.