This series of books for the EDEXCEL course are, in general, very good. I have taught myself a lot of modules purely from these text books. How ever, some advice for anyone planning to do it with Decision 1:
1. This book has a LOT of waffle, you will waste so much time if you try and finish all of this book because it's not necessary at all. Skip most of the questions, move on when you're good with a topic.
2. There are a lot of mistakes in this book as another review mentioned - if your answer disagrees with the book then use the internet to double check it.
3. A lot of marks in Decision 1 come from the ability to correctly format your answers, make sure you pay attention to the sections of the book that show you how to do this correctly.
I like these text books a lot but in my opinion this one is the weak link, personally I would stick to Statistics / Mechanics after having tried them all. Good luck.