Warning: This is all second-hand knowledge that I've gotten from reading too many threads instead of actually studying for the MCAT. I haven't actually taken any NS FLs.
I think NS changed the most egregious parts of their FLs after the initial outcry. There's thread on here (I think it's called something like LOL NextStep) where users were saying that they found one CARS passage that was exactly taken from the AAMC material – except they replaced "doctors" with "lawyers". Someone (in one of the recent MCAT threads – I follow April 2016, May 6 2016, and May 20 2016 LOL) also mentioned that NS 5 in particular had some very specific questions that matched AAMC questions as well.
The "bad thing" is that if you've taken NS before the AAMC FLs and reviewed questions that were too similar to those on the official materials, then your scores may be artificially inflated because you had essentially reviewed that question already. I'm not sure how big of a deal that is (besides the whole, plagiarism is wrong thing – especially if you're profiting off of it!), but at the higher end of the scores, getting an extra 1-2 questions right may mean going up 1 point that you wouldn't have otherwise.