I have found all of the "For You" books to be absolute lifesavers for my Science IGCSEs. They were the only books that explained everything on the syllabus in a concise and easy to understand way, without including unnecessary information like many other books do. In addition to this, it is not like the last minute CGP revision guides. It can be used to teach you the concepts from scratch if you want to self study topics at home before learning them in class.
The "For You" books have helped me a great deal in achieving 3 A* between my 3 science IGCSEs. I took the Separate Science course, which is more challenging than the Double Award, and gives me 3 separate results as opposed to 2 combined. The book indicates where you don't need to learn the stuff if you're just taking double award, although you should always refer back to your specific syllabus. I got the syllabus of the Edexcel website, as I took the exam with their board.