The problem with the Nook, and I have one and like it, is that Barnes and Noble is a company at risk now. They're losing money very rapidly and that's been getting worse each year. A lot of pundits are saying this could be their last year. Of course the pundits said that last year but who knows.
In either England or Europe, I forget which, maybe both, B&N pulled out a couple of years ago and left their customers with Nooks either with no access to books or limited access. I don't recall the details now.
A bunch of years ago B&N went into the ebook business in the days before cell phones and tablets and ereaders. You downloaded their app to your PC and you could use that to buy and download books. I installed their program and bought half dozen or so books. I read them all and they weren't books I was likely to read again so when, after 2 or 3 years, they announced they were getting out of that business and we had 30 days to download our books, I wasn't too worried. I downloaded my books and a few months later I got a new PC. The app was no longer available so even though I had the books I couldn't read them. No big deal. There weren't many and I'd already read them. But there was an important lesson there.
A lot of people lost a lot of books. I was one of the lucky ones.
Probably today Amazon is the safest source of books. They're big and stable and not likely to go away any time soon. But things change. Just in case I make safe copies of all my books.
You don't have to be a tech wizard to use Calibre to make backups of your books. Anyone who does it can easily show you how. There are videos on youtube that will show you how. There are several steps but nothing difficult. If you can follow directions to Walmart you can handle it. You just do the things the videos tell you to do to set it up. After that doing the actual conversion is trivial. It's as easy as eating a hamburger and a heck of a lot faster.
Barry