Fantastic resource on Arabic grammar. So far, it has been the best at explaining the Nominative, Accusative, and Genitive cases in MSA. It was also able to fill in gaps in my knowledge of Verb Forms and Verbal Nouns. Unfortunately, it doesn't have the explanation for conjugating verbs in the past and present tense for the dual feminine form, but admittedly, that is a pretty rare concept, even in Arabic.
What I learned from this book: I can get through a book called 'mastering Arabic grammar' and master next to nothing.
This book is very good for quick (and broken) Arabic for every-day situation. It's a good first book, but with the complexity of the language (up to twelve verb conjugations and a vocabulary unfamiliar to the non-Arabic speaker) what is needed is a good primer in the old style, i.e. with little bites of grammar and lots of exercises.
Could do with a bit of proof-reading but otherwise it's excellent, and sits nicely with the other Mastering Arabic books. It covers all the basic grammar topics to do with nouns, verbs and adjectives, so it's good for intermediate level practice -- but if you need to know about more advanced grammar like complex predicates, subordinate clauses, modal verbs, etc., you should probably look elsewhere.