CGP have always been a preferred resource for me. They manage to break down concepts very clearly, without the need for pages of waffle, and as a parent remembering this stuff for the second time around it is very easy to follow.
The complete revision and practice guides are definitely worth the extra money. This one contains all of the information from the revision guides, additional warm up exercises and exam fragments at the end of each sub-section which allow the student to review the new concepts immediately. Also there are revision summary questions at the end of each section and mock exam papers at the back of the book.
I also bought the workbook and answers as a suppliment to this book which has hundreds of questions and answers that can be photocopied and given to the student to work through as practice makes perfect!