I just passed my Zend Certified Engineer test. It wasn't easy. For preparation, I used both the Official Zend Study Guide (by Zend Technologies) and this book. I often found myself frustrated by the numerous errata in both books, but there were significantly more mistakes in this book (ranging from having the wrong answer listed in the answers section to typos). The positive aspect of this is that it forced me to spend more time with the online php manual answering my questions. I found the questions on the actual exam to be more like those in this book, than from the Official Study Guide, but you really need the Official Study Guide to make some sense of the answers in here as well. There were questions in this book covering exam topics that wheren't covered in the Official Study Guide. That's reason enough to get it.
The print quality on the pages is sub-standard, but the questions and thorough answers were very helpful.
Simply put, I wouldn't have had any chance of passing the exam if it weren't for this practice test book, even though it's aggravating at times.