I thought it would be hard and I was right. It was bloody hell! Really just the Further Pure modules, all the others are alright. But man, I really just gave up in the end. I took it as a fourth A2 and couldn't focus on it properly (there were other non-academic issues too which distracted me) which made everything worse.
It is hard, definitely the hardest of all my subjects, and much much harder than Maths A-level (which was a doddle tbh). Looking back, I really wish I had spent more time on it, because it was just the FP2 and FP3 grades which completely failed me.
If you're willing to work for it, then yes take it.