#2
I dunno, since I don't have the book. I have Troy Stetina's Speed Mechanics for Lead Guitar, though, and it definitely helped me back in the day. I'm assuming this book is at least a bit more theoretical than his Speed Mechanics. Troy's supposed to be a really great teacher, though, so I don't see why you wouldn't want to get it.

You should look for reviews of the book on Amazon or something and see if you'll like it. That's generally what I do if I'm not sure about a music book.
#3
Holy Katana pretty much says it all. Troy has a great reputation, so if the user reviews you read are mostly positive, it's pretty much a safe bet to buy the book. I've used Speed Mechanics as well as some other, less complex books from him, and they were great books to learn from.
A samurai once asked Zen Master Hakuin where he would go after he died. Hakuin answered 'How am I supposed to know?'
'How do you not know? You're a Zen master!' exclaimed the samurai.
'Yes, but not a dead one,' Hakuin answered.
#4
I own it and consider it definitely worth it. Alongside Speed Mechanics, you'll learn a lot. He begins with intervals and ear-training, then moves to scales, then triads, etc.... goes into harmony and his examples are very well written and recorded.

It'll take you a long time to get through it, but I'm about a 1/4 through and really like it.