If I'm honest, I'd bet they'll be out of the game in two years time.
I could see them being eaten by Amazon. Especially as most startups these days just make these apps in order to be gobbled up.
Kinda like Catch Notes, which closed up shop recently not because of money/userbase issues, but the fact that Google, Apple, Microsoft, Evernote, and the others turned a blind eye and didn't want to buy them out.
It doesn't have margin controls, and to get to the next page, you have to swipe like you're reading a webpage.
But again, I like the recommendations, and the app itself looks very nice. I enjoy it even without the customization that Marvin, Freda+ (on my Windows Phone) have. It's still superior to the Kindle app in that sense.
For one thing, you can actually COPY & PASTE. I find that weird, being that this is a DRM'd service.