I recommend it highly for ESL speakers who have finished their formal ESL instruction or who are in an advanced level. They should use it the same way they do a dictionary or thesaurus - as a reference book. There are numerous grammar explanations that are easy to understand. Azar provides several lists that students can use as a reference if the grammar rule/pattern is an obscure or difficult one. It has a series of charts for students to visualize the actual time that the different English verb tenses cover. Azar covers a great deal of material, but the book is only 140 pages total - small and thin. That makes it convenient to carry.
I also recommend it highly as a teaching aid when instructing native speakers in reading and writing so that teachers can more fully understand English grammar from the ESL perspective. When I teach developmental writing to college students, I find that I am oftentimes dealing with native speaker dialect issues, so an ESL explanation can be more appropriate. In addition, there are many ESL students in Freshman Composition courses, so the instructor needs to know how to help those students.
The Chartbook is a reference book. If you want the exercises, get the regular text or the workbooks. Azar has been criticized for presenting grammar out of context. I believe that is a valid, although not a shattering, criticism of her main texts. However, this is not supposed to be that sort of book. It is supposed to be a reference book, and the grammar will be out of context.
I recommend this book unreservedly.
Karen Keyworth