It entirely depends on you, really. Forget GCSE maths, only people with A*s at GCSE were allowed to take F.Maths at my school and a third of them are struggling (there are only 6 in my class). One is probably burdened by a language barrier (she speaks English fine, but she's an exchange student from Norway and might not have the best grasp of mathematical terms.). The other one, however, is finding things quite difficult, most notably the speed of it (to be fair our school only gave us one extra lesson for F.Maths, otherwise we have the same timetable as regular maths). Then there's a sort of middle ground in this class, with people who find some topics easy, others slightly difficult, and then there's myself and one other who don't really struggle
I would argue that the reason we don't struggle is that we learn the topics out of class, unlike that second person I mentioned, who whines that teachers don't explain things fully and to his liking exactly, which is a ridiculous expectation given our time restrictions.
(We're doing AS Maths and F.Maths in Year 12, A2 for both in Year 13, unlike many schools.)
tl;dr - take f.maths and if you can't deal, drop it, if you can