I still think my points are valid, in that you have less risk of losing access to your pottermore book due to the lack of DRM, it does mean you've to break a cival "contact" to keep your books safe although that's a little better than having to break anti circumvention laws, however I'm really shocked they would even attempt to block people from making backups in that way.
It's a clause that is in no way needed. The terms should be about ensuring people don't have the right to pirate the books and just give copies away. Not about how you keep your purchase safe.
I'd go as far as saying it's the most idiotic and monumentally stupid clause in any T&C I've ever read
I hope they have a change of heart and remove that clause. Not that anyone will follow it.