i take edexcel maths and further maths
i would say that the graphical calculator is 100% worth it - it saves you so much time and the exam questions are written with the assumption that you have one so you don't get many marks for things you can do with the calculator e.g. simultaneous equations, solving polynomials, matrix multiplication, stats etc
my school required us to buy the pearson textbooks for maths and further maths - they are really good, and they have everyhting you need in them as well as questions - if you are buying these, then you probably don't need to bother with the cgp books