If you're talking about the regular EK review books, then yeah, you're right, those questions within the chapters are tricky. But I don't think that's a bad thing. Perhaps they're more difficult than the actual exam, and maybe some are even based on slightly esoteric knowledge that isn't completely necessary. But if you've done harder questions, having easier questions on the actual exam will probably ease your nerves alot during the test.
Whenever I used to take SAT II exams, I always used Barron's, which were, and are still considered the books to use if you really want to be overprepared for the test. The questions were trickier, some concepts slightly more detailed than needed. But on the three main SAT IIs I took, I got 800s, because as soon as I opened the test, I was immediately calm, with questions I could tackle easily, thanks to my overpreparation.
Sorry, that was super long, but basically, I think those questions are worthwhile, and at the very least, the 30-minute exams are definitely worth your time. 🙂