I have (and have had since near the release of 2014) the 2014 E book.
It gives you a lot of the functionality that the older CD ROM versions had. All places where another code section is mentioned is a link that you can click on and go to that section. Most instances where a word appears that is defined by NEC is bold faced, and you can click on that word and a pop up bubble gives you the definition. It also has links for pop up bubbles in places where there was a change from 2011 that tell you what was changed.
I found it easier to navigate then the PDF I had for 2011. The navigation pane breaks down to the 225.30 level and not just to Art 225, Art 230 level. Art 250 is a long section and is nice to break that one down further then just the title.
It is also an on line application, not limited to one PC or other device, you can log in with your user name and password from any device. Get a new computer or smart phone - just log in, no reinstalling or dealing with additional licenses for more then one device. There is special app for smartphones that is better tailored for the phone - but is a free app. The app is for Inkling, which is a third party that hosts other E books, not a specific app for NEC itself. Otherwise the base version is a web browser based application.
Not sure what changes may come with 2017, for the E-book or the PDF.