Finnish: An Essential Grammar by Fred Karlsson (266 pages long) is a complementary book to Teach Yourself Finnish or any other basic Finnish book for that matter. Why? Because if you don't know the basics of Finnish grammar, you'll get a headache when you start reading Fred Karlsson's book.
Of course you'll also get to learn about Finnish pronunciation and alphabet and some basic information about the Finnish language, but since this book is so comprehensive in examples and different types of changes in the Finnish language, you'll get information overload if you haven't grasp the basics in Finnish. So for that reason only, I can't rate this book as a 5.
Other than that, this book doesn't come with any exercise at all and that's a pity. But still I've found SO MUCH HELP from this book when learning Finnish. This book is designed so that each chapter focuses on a certain topic. For example: Infinitives, Comparison of Adjectives, Tenses, etc. Then it breaks down the rules and the exceptions and examples in sentences as well. So it's good in the way that you can not only see clearly the differences between different types of rules to form a word, but you can also see how the words are used in a sentence for a certain topic.
The bad thing is that it gives so much detailed information for each topic, so you may feel dizzy when you're trying to absorb all the information, especially if you're not familiar with the grammar terms. From my own experience, I only try to use this book according to the topic I'm learning at that time. For example: if I'm learning Past Tense, I'm not going to try and read about Past Perfect Tense since it'll only make me confused. However, I'm GLAD I have this book to turn to whenever I need it, so it's still worth buying if you're serious about learning Finnish.