Right now Oyster is iOs only and invitation only. So it is just getting started. But for $10 a month you can read as many of the approximately 100,000 books in its library as you want.
On the images from the very limited webpage, there are some very mainstream books including The Life of Pi, Starbuck’s CEO’s book Onward, Michael Criton, JRR Tolkien, Water for Elephants and more. But I have not seen a list of books or a list of participating publishers other than Smashwords. According to GoodEreader, Smashwords announced that they have 250,000 books in their catalogue and that all of them can be borrowed via Oyster (which makes me wonder if there were 100,000 books in addition to Smashwords or including Smashwords.)
I certainly read more than $10 a month worth of books, but my guess is that many of the books that I read will not be offered here. But I welcome a chance to try it out. You can request an invite here