I am a full-time IELTS teacher and have been using this book since it was published in my class on the Gold Coast in Queensland. This is a great book for practicing all aspects of the test in a real situation. In my class we use it on a regular basis.
I find the best way to use it is to first study a reliable text like "Foundation IELTS Masterclass", and then find a task from this text that can be used to reinforce the text. For example, if we study how to write a process essay in the class, I search for a process essay in one of the Cambridge IELTS books.
Cambridge IELTS 7 has the following writing task 1 question types:
Test 1: Table Test 2: Line chart Test 3: Bar chart Test 4: Pie charts