CGP books are nice to read and explains things well. They're are really good to get me into the revision mood, more than books that are full of tedious waffle and technical jarjon. But you shouldn't only use them and nothing else. I think they're really good for Languages and you can get CGP books with language vocab booklet and app to help you master it.
Other revision help are YouTube videos, a book specific for the subject and exam (EdExcel, AQA etc) that you're taking so you can practise answering the type of questions that will turn up in the exam. CGP won't cover that. The book should have fully worked answers in the back pages, not just the answer, if you're doing Maths. If you get the same answer in the book, it doesn't mean your working out is correct.
Avoid the Collins GCSE books (particularly their Maths books) because the answers are online instead of in the back of the book. If I go online during revision, bang goes my revision!