I have a Kindle Fire to replace an iPad. It was so slow in comparison (but a fraction of the price). The first thing I did was hacked it to use it as a tablet, installing the Google Play Store (by installing 4 apks, as I remember it). It now works as a very slow tablet, and I can install any app that I would be able to do so on my phone.
However, if all you care about is reading books I would first suggest the free idea of downloading the Kindle app on your phone and seeing if you can read a book on your phone. If you can, then go for the real deal and get the paperwhite tablet (which would be way better as it is non-reflective).
My mom still has the Kindle 3G I gave her way back when which had free 3G internet that came with it for about a decade . 3G is no longer a thing anymore though. But she adored it for all that time, reading hundreds of free books (there are thousands and thousands of free e-Books out there). But she also still bought regular books, too.
I myself bought the Nook from Barnes and Noble, used it for a few months and now it sits gathering dust in a drawer. Not even sure if Barnes and Noble still exists.
Alas, it was not for me. But they are awesome ways to take your entire book collection with you when you travel.
