I think it's a serious mistake that they allowed unlimited borrowers at a time, because that shifts from fair-use format shifting to effectively making multiple copies of the format-shifted document.
That said, IANAL and I don't know what actual legal conclusions were arrived at from the trial or appeals.
I think it's a serious mistake that they used DRM at all. That positions them right along the publisher narrative which is exactly where they should not be.
That said, IANAL and I don't know what actual legal conclusions were arrived at from the trial or appeals.