I bought this book primarily as a comapanion to A Japanese Reader: Graded Lessons for Mastering the Written Language (Tuttle Language Library), which was designed to accompany the Martin book. Only Lessons 18-30 of the Miller book are meant to be used alongside Martin, but they are tied somewhat closely. Though I have some solid experience with Japanese, I did find that there were a few forms in Miller that would trip me up a bit, and it was also assumed you would already have gotten the vocabulary from Martin (though it was somewhat rare for me not to know the words, as the vocabulary was mostly very basic), so I thought it would be worth having.
The book (Martin's) covers an enormous amount of ground very quickly. I don't think I could recommend it as a first book on Japanese, unless you were willing to spend quite a lot of time hammering in the knowledge from each page yourself. The book was chiefly intended for people who were already actually living in Japanese, and needed a roadmap to the language. Both the vocabulary and the grammar can be quite old, including terms that really aren't used so much any more, or aren't used in the same ways (this may have changed since; my copy is a used 2nd edition, revised in 1956). Still, most of what you see in this book still applies today.
The book does a very excellent job of explaining difficult and complex concepts as simply as possible, where many other texts struggle ineffectively to convey them. It also describes Japanese pronunciation much more accurately than I have ever seen elsewhere. I would recommend this for any student of Japanese who has had some experience with the language; however, due to its out-datedness and very, very brisk pace, I don't think I'd recommend it for new students of the language.
The book is both exhaustive and concise, which makes it a superb reference or grammar-refreshment book. Perhaps the best recommendation I can give it, is that it taught me more about Japanese in one book than I've previously gotten through several successions of college textbooks.