I've been working my way through Wightwick and Gaafar's other book, Mastering Arabic 1 for a month now, and whilst it's a great introduction, it is a bit frugal when it comes to unlocking Arabic grammar (you'll learn "it", but several chapters later you still won't know "that", or "this", for example). This is most likely to teach other fundamentals before you start pointing at the horizon.
After 7 Units of that book however, you should know the alphabet, be able to read most Arabic, and if like me, you'll be hungry to actually read something substantial, yet frustrated that you know an extremely limited vocabulary (why is the word 'Donkey' so prolific in language guides?). Even with a dictionary, the grammar can trip you up.
Enter Easy Arabic Grammar. I bought it so that I may read at night, helping to reinforce the previous lessons, and prepare me for the later ones. It has exercises, but they are so far simple enough to do orally or in my head, and after spending 45-90 minutes a day with the other book, I just don't feel like working!
I would give it 5 stars, but kindle users beware: There are quite frequent formatting and quality issues with the Arabic script. Script, pictures, and English text that forms part of an image is of a lower quality than I would expect, though without the print edition, I cannot say if this affects that too. Arabic script appearing along with the English text is (thankfully) scalable, however there are formatting issues, with words being broken apart, most likely due to the Kindle's justified text alignment.
Neither of these issues are very problematic if you can read the script, as you'll be able to piece together the words by the shape of the letters.
I would not recommend the book on its own, or as your first Arabic guide, but it's very good so far in filling in the pieces I've missed from the main lessons.