First, don't pay $150+ for this book. When I registered for my Praxis II exams, I immediately purchased all of the study guides. ETS charges less than $30 per study guide! I think it's insulting that people are trying to sell it here at such a ridiculously high price; check out the ETS site and buy it new for a fraction of the used price you're finding here, Google it, or borrow it from a classmate who passed the test - that is, if you really feel you need it.
Now, how good are the guides themselves? I have to say that I skimmed the first one to prepare for my first Praxis II exam and found it horribly intimidating. I didn't think I had a prayer of passing when I looked at the study guide, but I didn't find the examination nearly as difficult as the guide led me to believe it would be. My tests involved a lot of "horse sense" and questions that you had better be able to answer at this point in your collegiate career. If you can't answer them, either you must suffer from serious test anxiety or you have been wasting your tuition dollars.
For the other two exams I didn't use my other study guides and passed both tests the first time, one with a perfect score. Seriously, my advice is to listen to your professors in class and go over your notes that you took in class. Reality is that any decent professor will have pointed out the things that are likely to appear on the test anyway, and would have (without giving specific information) provided you with everything you need to pass your Praxis II examinations. This is what we pay for when we go to college. You shouldn't need to cram for these exams; by the time your down to your last semester of college, you should already be able to pass the examinations without additional study.
If you're good at taking standardized tests, don't waste your time.
If you struggle taking these types of tests, you can buy the book to make you feel more confident (but don't pay more than $15.00 for it!)... but you're probably better off reviewing your notes really well.
If you fail because you didn't know the answers, go kick your professor.