It turns out that while the HP ebooks are DRM free on pottermore, when you buy them and send them to your Amazon or B&N account, they get DRM added to them. Which means if you download them directly to your nook from B&N, you will only be able to use a nook to read them, forever and ever, just like the rest of your B&N books.
Downloading them as an epub to your computer and then sideloading them onto your nook with ADE supposedly keeps them DRM free so they will work on any ereader device. This means that should you ever get a different ereader, you can keep you HP ebooks without illegaly removing DRM from them. I thought I would share this because personally, I think the option to have an ebook compatible with different devices is very preferrable to one that only works on my nook.
You can also download them up to 8 times from the Pottermore website, so you can send them to your nook for the convenience, and then download directly from the website for backup and future-proofing (and still hae 6 more downloads available).