Hey,
Last year, I took the GCSE Level 2 Further Maths exam for AQA and I'd say that it was quite easy, and it puts you in REALLY good stead for when you study Core 1 and 2 if you decide to do Maths at A-Level.
I've also done some Additional Maths papers, although I didn't sit an exam for them. I found it generally a lot harder that further Maths, but it's a matter of opinion.
Good luck!