Sandi Metz has another book on what I would guess is a similar topic, Practical Object-Oriented Design in Ruby (colloquially, POODR). I found that book to be highly practical to daily development and I expect this to be no different. You might try googling for info about that book or perhaps try the mailing list if you want to find out more before buying.
I'm curious about how the two relate to each other. Is 99B supposed to supplant or complement POODR?
This is designed for people who just pull out their credit cards and buy the book. I would expect she and Katrina have a significant number of those folks. No preview needed.
I doubt the lack of preview is intentionally some sort of loyalty/"in-crowd" test.