$40 seems really expensive for a short book like this. I'd love to read a few objective reviews to see if it's worth the price.

For $10 I'd buy without thinking. For $20 I'd probably buy with an Amazon type consensus. But for $40 I'd need a few trusted reviews before a blind purchase from a self publish.

Not that there's anything wrong with self publishing ... just that there's no judge of content or quality as there isn't a "style" for the publisher.