I thought NMS was the same as the real thing. I think the explainations were very good. It seems like there are a lot of OB/Gyn questions in NMS, but my Step 2 had tons of OB on it, so it worked out well.
I did not use anything for questions other than NMS and it was fine. But read something as well, like Boards and Wards, First Aid, or Crush the Boards. Don't just use NMS.