Sure the iPad air makes a fine ebook reader however if your primary use case is this you may want to save yourself a few bucks and get a kindle.
For journal articles, textbooks and most PDF documents, the Kindle is useless.
I have a Kindle and it's great for reading novels. But that's all it can do. Hard to justify carrying it around for that single function. Paradoxically, I carry the "heavy" iPad when I'm on the go, since it's a multi-purpose device, and keep the much lighter Kindle only at home for reading novels..