Well i've just completed AS's in maths/physics/accounts/general s. /economics
and achieved AAAAC respectively, and have decided to drop economics due to not enjoying it, and taking up an AS further maths this year.
for AS maths i did C1/C2/D1
this year i'm doing C3/C4/S1 for A2 Maths
and for AS Further maths FP1/M1/D2, alongside A2 Maths
in january i'm sitting FP1 - before learning any of C4.
Basically for FP1 knowledge is only assumed on C1/C2 so you can do it with just AS in maths as i am, and obviously the applied module wil be the second applied to the one you did at AS... so mine is D2.
I am doing it because i'm planning on applying to do a maths degree, and obviously further maths will be very beneficial and i think i can get a grade A in it aswell so i'm doing it. Yes, its definitely worth it and definitely possible.
I say: go for it like i did