@murg. I agree they are likely doomed. It is one of those good ideas in theory which founders in practice. They are chasing a market who shops in physical stores, perhaps sees a physical book and wants the ebook. They are hoping that the person will effectively buy the book then and there in the form of one of their cards and go home and download it. I suspect a more likely scenario is that the person sits down, orders a coffee, connects to the shops wifi and downloads the book to their device with a click or two.
Your quote from their terms and conditions is horrifying, and there are other similar provisions. I particularly liked:
Upon closing of your account, or change of ownership of a reading device, all titles received from Enthrill must be deleted from your device(s).
No thank you.