Can't say about the HDX but my wife has a Kindle Fire and she's not impressed with it . It does all the E-Book thing but she still prefers the basic Kindle for this. As a Tablet its OK but is locked to Amazon Apps etc. I'd stick with the Samsung (which I use) and find perfectly good for E-Books as well as having 2 cameras.
Surface Pro 5 News - release date, UK price, features, specs