I bought NS 1-4 recently. I have only taken #1 so far but it was pretty good and matched the AAMC material I have done closely IMO. Glad to hear it gets better as I will go 2-5. As for the exams 6-10, I did not buy them yet, and I may not if I do not need them. Likely many people never get to all 10 NS exams or 12 Kaplan/TPR exams and, as a result, you will not find much discussion of them on SDN. Don't forget, SDN is but a fraction of a fraction of the MCAT population.
I do know a few friends who took a Kaplan MCAT course in Spring and said that their #10-12 exams were much more difficult, with more obscure AAMC topics on them. I imagine NS would do the same, as does TPR. After 6+ exams, they are going to have to move on from the high yield topics and start testing us on the more rare MCAT material. To me this would have to effect the curves and difficulty level perceived by any given student. Also, we only have 2 AAMC exams, so knowing what is truly AAMC like is tough with so little info. Does the tone/style of the NS exams change radically after 6? That would help me decide if I want to purchase them.
There is a table/thread which shows how well any companies FL exams stack up and predict performance on the AAMC practice tests. It looks like EK and NS come out at the top, but again, its all limited to SDN people inputting anonymous data. I will likely buy 1-2 EK exams if I still have the $ and sanity required by December.