I like the methods using for learning MSA. It's not the only book related to Islam religion, but actually all Arabic is related to God's believing. That I advice you is to know them, because we usually use them in our dialy life. Therefore, it's not all Arabic, you need to check vocabulary words from different sources, because like that you make more progress in Arabic.
Another thing to add: this book is designied to Arabs or foreign people who just convert to Islam, in that case you find some parts on it about Quran, some kind of rules in Islam which seem it's all about Islam, but just few parts on it. For me, i have been using it to know different ways for explaining to my students. Just remember, Arabic has a large vocabulary, so missing one part of it, you will always have problems with :)