I did iGCSE and I found the jump to A Level not that bad at all. I was actually predicted a B for maths, but that was ridiculous and the teacher was meh, but I knew I could do A Level maths, and was even recommended to do further maths when I started. But becasue of this B, I was compelled to do a lot more work in preparation for A Level, and to get an A* at GCSE.
The questions are very different to A Level, i'll give it that, but the first unit of maths is definitely an ease in.
I definitely recommend you to do some more work, and find how you find GCSE first.
Hopefully I helped answer your question? =S