I went heavy on the sample exams in my prep. I've gone through both PPI samples, the 5 Spinup samples, all four CI samples, and the NCEES sample twice apiece. Overall, I think each source has their place. I tried to imagine preparing with only one of each resource, and I really don't think you can cover everything with just one.
- I think the Spinup problems are the easiest overall. They are also by far the quickest to get through, since there is very little calculation involved in a majority of their questions. Also, by the time you get to the 5th test, you feel like you've seen about 70 of the 80 questions in the other four tests. The repitition does help to drive certain concepts home, but I think the limited scope would definitely hurt if this was your only resource.
- The Complex Imaginary tests were more difficult than the Spinup ones, and the questions involved more calculations overall. These tests also seemed to cover a pretty broad range of topics, which I liked. Each of the four volumes felt unique to me. I don't regret only going with one or two. They did a good job with these.
- I thought the PPI samples were pretty tough. For the most part, though, it seemed like the difficulty was more because some of their topics seemed very obscure, and that unfamiliarity made things tougher. I do feel that these were the most involved and difficult NEC questions that I ran across. I haven't seen that CI NEC book that just came out, but I learned quite a bit just by reviewing these questions. I didn't get that from most other practice tests, where you typically just need to look up one thing per question. The obscurity of some of these questions would make things difficult if this were your only resource. I did like how familiar I became with the EPRM while doing these questions, since most answers could be found if you dig deep enough into that book.
Obviously the official NCEES sample is going to be the most realistic practice. On thing I will say about the difficulty of this test is that it seems like they put a lot more effort into the incorrect answer selections than any of the third-party sample exams. In most CI or Spinup problems, at least a couple of the incorrect answers would be fairly obviously wrong. In the NCEES sample, I found it more difficult to weed out the wrong answers.
Take this review with a grain of salt, because I've still got 2 weeks to go myself! Having done this many sample exams though, I do feel very prepared for anything they can throw at me. I'll try to follow up after the big day, hopefully not to eat my words!