Well, they're probably not profitable. I couldn't make money serving myself this way
I figure if we are paying $9 a month and they're paying $3 a book read (average?) giving us 3 plus a freebie would probably break them even.
I expect their Selects to be well-reviewed but perhaps very long books. Literary and non-fiction maybe. Not a lot of genre. Plus some inexpensive ones, but mostly time-sucks. That's what I would do.