Earlier quoted context omitted.
I buy physical books because they're cheaper than ebooks. I'll usually pay about $.50 to a buck for them. Sometimes my friends just give me a box of books they're done with. The local thrift store often has bestsellers for a buck. The usual price for a used book on Amazon is $.01, which with shipping comes out to still far less than the ebook.
For ebooks, Amazon already has one free "rental" per month of select books, for Prime members. There are other good sources of free books include this blog: http://www.sfsignal.com/archives/category/books/free-fiction...
I don't like losing access to things. If it was "you can download one per month and keep access as long as you're a subscriber" sort of the way Playstation Plus works that would be OK with me.
But the rental program feels more like a cruddy crippled library than a real service.
I'd rather pay the $5-$10 for the eBook and not have to deal with it.
This new service is interesting. I don't read enough for it to be useful, but I could see it saving my dad quite a bit of money (or trips to the library) if they had enough books.