I took level 1 a few years ago, and failed by 4%. I used the vocabulary book in this series and did very well on the kanji, vocabulary, and reading sections of the test. Unfortunately, I only began my prep about 3 to 4 months before the test and didn't have time to go through this book - only wish I had!
If you want to pass the level one Japanese Proficiency Exam, this is the way to go. Buy the others in the series as well. The book consists of practice exercises similar to the problems that appear on the test. The problems in the book are designed to be just a bit harder than the ones on the actual test, so you know that if you can consistantly score over 70% on these exercises, you have nothing to fear. YOU NEED THIS BOOK, because it will teach you the specific grammar that appears on the test. As some of these constructions are fairly literary, formal, or otherwise obscure, you might not learn this grammar elsewhere.