I've never heard of that site but there's quite a few book 'rental' sites.
BooksFree is the first one that comes up in a search, but there's also Bookswim and another site that I remember seeing that just had romances but now I can't find.
I wouldn't use the service though because I like having a bunch of books to choose from. I would be annoyed if I had to select the books I thought I might feel like reading in advance.