Having watched 100+ students take Altius 1-10 and examined their scores, there's not a difference between 1-10 in terms of overall quality or usefulness. I think you're looking for something like "6-10 aren't as good, so stick to 1-5." I think about 1.5 years ago the Altius curriculum team was in the middle of updating all 10 exams and, since they went in order 1 through 10, some students taking exams during that time thought 1-5 were easier/better. But, as of this last cycle, I couldn't see anything to suggest that I'd rather have a student take one group over another.
That said, there are some of the 10 exams that are intentionally more difficult, some less difficult, some with more calculations, some with less, some with more physics, some with less, etc. That is done on purpose because the real exam forms vary in the same way. I would suggest you do as many as possible to get exposure to all of the different "types" of exams you can get on test day. My students usually find FLE3 and FLE10 to be the most challenging.
