Drop ATX last minute to attempt APM instead

You can certainly cover the APM syllabus in a month and a half but be aware it is also a very large syllabus, I would say bigger than ATX. The frustrations with this paper (from my experience) tend to come from the fact that big questions are often asked on such small parts of the syllabus so you really need to know EVERYTHING in a decent amount of detail. I actually preferred ATX much more than APM but that’s probably because I’m more of a structure and systems person where I like to do set calculations where as with APM it’s mainly theory based. The thing I’d say is ATX is harder to pick up at first but easier to master where as APM is easier to pick up at first but harder to master, if that makes sense?

I think that you need to decide which you really prefer. Are you a calculations person or theory person? And where do your main interests lie? Tax, financial management or performance management?
I have no experience of ATX but no one is easier between APM and AFM.
APM is definitely theory based with a lot of interesting facts you can pick up relating to day to day operations, while AFM is not just figures but really technical. In my opinion, APM is easier on the brain while studying. You just need to ensure you master the techniques required for exam sitting. AFM, can be very tough on the brain and its advisable to make sure you give yourself at least 3 months full study to attempt AFM as the syllabus is very wide.

All the best.