Advantages: I can take 5 or 6 books with me on vacation, all in the space of one very thin paperback, on the Nook.
I can take it to the beach or pool or car trip or anywhere, just tucked into my bag. (Of course be careful not to get water or sand on it - so far, not a problem.)
I love the "bookshelf" feature, where I can put all the books I've checked out of the library in one place.
Note: using this feature is a little weird. When you download the Adobe file on your computer, prior to checking out a library book, you can make a "bookshelf." BUT - that bookshelf does not get translated to the Nook! It stays just on the computer.
You have to make the bookshelf specifically on your Nook after downloading, and click on the list to make your choices of what to include.
The reason you want to do this is because Barnes and Noble is always transmitting to your Nook "new books for you to try," which include a chapter or two of a whole bunch of books. This (IMHO) clogs up my home screen, where really I'd prefer to just see the books I've checked out of the library and want to read. The "Bookshelf" is what I have to do to easily find them amongst all the B&N samples.
Eh - it probably sounds complicated the way I've described it. It isn't really, it's easy, just so you know your computer will hold your booklist in one way, and the Nook in another.
ANY-way, size, portability, easy reading, matte screen, dedicated device, and lower cost, are the pros for having an e-reader vs. a tablet. Better screen appearance and being able to check books out of the library are (to me) the advantages of Nook over Kindle.