I never studied any grammar at school and dipping into a German grammar book was quite daunting! They always assume a knowledge of basic English grammar when words like "accusative" and "dative" would be lost on me. On the other hand I didn't want to read 100s of pages of a dry English grammar book, and then go back to my German.
It starts off explaining what verbs and nouns are - obviously easy, but seeing written definitions and the different types of verb sometimes helps you spot the rules/differences in German more quickly. It ends up on advanced topics and is very comprehensive. I think it would suit most levels.
Every chapter is laid out clearly so a beginner can read it from start to finish and understand. You could also dip into it at random as you need or go back and reference tables and key points to refresh your memory. It explains how every language structure works in both English and German, giving examples for both, so you don't need to flick between any other books, even though in it's title you might think the book only covers English grammar. There are a few questions at the end of every chapter which I've sometimes used as a self-check, but it's not a patronising text book padded out with exercises.
For minute/advanced details the book points you to look in your German textbook, but I think you could get to a very advanced stage on this book alone. I haven't opened my German Grammar book yet. It doesn't give you lists of every irregular verb and things like that, it sticks to the point - grammar. The book is about a cm thick and you can take it anywhere, read on the train. It's really increased my understanding and confidence in my German, I thought I'd never get the hang of the grammar.