Is this the same as the Lending Library you'll get with Prime, where you can get 1 book for free per month if you're Prime customer? If so, the offer in Germany is absolutely terrible. I found only 2 books in that library, because they count endless self-published garbage-titles to their library of "600,000+" titles.

From the comments here, I assume that the model is similar in the US and 9.99$ is only so cheap, because there's mostly junk in the library.