Yes, it's true that the CRP-5 is used for the exams, but - they use three of them to get a proper average because the build quality used to be so awful (although it seems to have improved somewhat). That means there's plenty of scope for alternatives, although the text on the faces seems to be more relevant on the CRP 5.
My own weapon of choice is the Jeppesen CR3, but of the two you mention, the ARC is what I would choose if I was spending £70
phil