I'm a relative beginner probably been studying hardcore for a month or two (intensively). Mainly focusing on just getting a gist of the grammar. I think I'd weight myself between Intermediate to low Advanced in any other simpler language by now if I had ever put this much effort and spent this much time/money on language materials, but alas German is a language of difficulty with it's many nuances and many tricks, unconventional methods, and exceptions. So much so, that I've studied a couple of languages and this is the first ever where I've had to make grammar flashcards!
Anyway, this book is pretty nice for beginners to intermediates who need a semi-reference like information written by a native speaker. The prose is non-linguistic for the most part and very casual which may be a plus when your in the learning stages for some persons. So far I'm only 1/3 thru but I've seen many of the grammar notes that were cursorily mentioned in other books, already listed in the first few chapters. As I read further and skipped ahead though I noticed the book diverges off from being just grammar into common mistakes and "awkwardnisms" that learners make like "ich bin kalt/warm" which looks like "I am cold/warm"...but actually means "I am cold-hearted/gay"
Overall, so far I like it, I cant compare it to 1001 Pitfalls which seems to be along the same lines because I havent received it yet nor can I can compare it to Hammers Guide because I understand that's an academic book and is prohibitively more complex and formal. Though as it stands this is good as a casual, easy to carry, non-brain taxing, review or preview to chapters (in a real accompanying grammar book).
NextDayEdit: So i just recieved Henry Strutz 1001 Pitfalls in German and to say the least I like ten times better so far. I've learned more nuances about the German language and grammar thus far than any other book I've used so far. I really do like that one. The only thing is that that book isnt as casual as this one and is slightly older but in terms of breadth 1001 Pitfalls covers quite more and seems more thorough. So I'd cop that book as well if your interested in grammar.