I agree that this book includes a challenging range of material, and helps you to assess your writing. However, I, as a native speaker who is unofficially helping someone towards the IELTS exam, worked through the first 40 or so pages and found 5 or 6 serious mistakes, mainly in the reading section: not spelling or typos, but errors of fact in the answer key and in a graph key. The first paper has hidden answers that you are supposed to find as you work through, but they have omitted some. They are not there at all, giving the impression that in a certain paragraph naming exercise, 2 headings per paragraph are required. No, they simply didn't get round to finishing their explanation of thought processes and telling you what the final decision should be. You will need a native speaker to help you if you use this book.