Aaron Shepard's Aiming at Amazon is intended for a very specific kind of reader: someone who has self-published a book and wants to maximise its sales through Amazon.
More specifically still, the book is designed principally for those who have published non-fiction; and, if you follow the author's recommendations, you will also have used the services of Lightning Source.
If you already fall within this target readership, then there is no doubt that this book is worth its money. In fact, it's probably worth ten times its money. There are pages and pages of advice and tips here, most of which will enable your book to move towards achieving its potential, and, in so doing, generate income for you.
If you're still thinking about whether to self-publish a book or not, then reading this guide is an even more salutary experience for you. I don't think I have ever read a book which made it plainer that publishing is damned hard work. It's a fiddly, irritating, time-consuming and exhausting rigmarole of paying close attention to tiny details, adjusting them when they don't turn out right, and then discovering that you have a dozen more of the same to attend to. Not, on the whole, a lot of fun. Writing a book may be fun, but publishing often isn't.
Since Aaron Shepard is an American, the whole book is orientated towards American practice, and refers to American firms, such as the giant distributor Ingram. But even for writers and publishers from other parts of the English-speaking world, the US is still the biggest market, and so the book remains highly relevant.
I think that's probably all you need to know. But let me emphasise, again, that this book is absolutely brimful of technical, hands-on advice on everything from choosing a sub-title to designing a cover to setting a price. As for Amazon itself -- well, I had no idea that there were so many different facilities on offer, or that they were capable of being used in so many different ways at the discretion of the author/publisher.
All you need is endless time and patience.
Aaron Shepard makes something of a habit of writing how-to books for writers and small publishers. His Perfect Pages was reviewed here quite recently. He also offers a web site which includes updates on his various books and links to more resources.