Anyone who's done both Barbri and the NCBE questions want to weigh in on the differences? I'm doing my first half-day practice on the NCBE questions tomorrow.
TL;DR I think they're a bit easier but have more variation in format. Also, I didn't bother with the last few MPQs after hearing how stupid they were.
I just spent the past few days doing a ton of them, and overall, the most notable thing is the length. Real ones are, on average, WAY shorter. Tons of them are 1 to 3 lines. There are still the annoying-as-balls page-long property ones, but they're not as common. So if your timing is good for Barbri, you'll have plenty of time for the real thing.
I think they are easier than Barbri ones because in general they not only test more general stuff that isn't buried in the CMR, but also because they have clear, obviously correct answers. There are some super nit-picky ones though, and some annoying "this answer is right but not the best," as well as some that you just have to assume the right answer is what the question assumes, which can be annoying (e.g., B is right because the evidence is admissible for X, even though there's no facts about what exactly it's being offered for).
I've noticed a few formats that I've never seen with Barbri. There are some really difficult ones that give you a list of 3-4 concepts and ask which ones are relevant, which ones will be decisive, etc., and can be just one or all 4. Those sometimes take wayyyy longer. There are ones that give you a hypo and say why is this the correct result (e.g., Congress regulated something in interstate commerce = the commerce clause gives Congress the power to regulate interstate commerce). Another tricky one are criminal questions that give you a short hypo and the result and then 4 hypo cases to apply as applicable precedent.
I am really glad I forked over the money because it was a really helpful way for me to study. If you're interested in the site, PM me (so mods don't think I'm spamming).