I hope I am not "bumping" old threads. Is this an old thread?
CGP books are great for a quick review but is not good if its your ONLY AID for your gcses. I'd say a combination of your textbook, notes and CGP for each subject will definitely get you your marks!
I must say, however, the organization in the GCSE Biology is horrible. For homeostasis, there are information in page 20, and information in page 137. Also for the heart, there are information on page 201 and 134. Why can't they organize things more efficiently so students don't have to keep flipping around?
But overall, they're quite good.