This was an ongoing internal debate I was having with the iPhone 6 and placing an order for a 6 Plus (for testing obviously) should I grab the iPad Air 2? After a few minutes I placed an order on October 16, 2014 for a Slate Grey 64GB iPad Air 2, it made sense to do so...for testing of course.
For the past 2 years I've been using the iPad Mini and while the iPhone 6 and more-so the 6 Plus removes the essential need for the Mini it doesn't necessarily remove the need for the iPad Air 2, but it all depends on what a person's use-case scenario may be. I work on several things throughout the day, week, month.
I use my iPhone 6 heavily, and my regular day to day machine is a 13" MacBook Air, but the iPad Air 2 is fitting into my workload without issue. I still read my regular magazines from the Newsstand app (I'm probably the only one to still use that app), Paper by Fifty3, several eBooks in iBooks, Lynda, Longform, and when traveling on the train or plane watching movies and TV shows on the screen is a nonissue.
For me it's the perfect companion device that I've come to use regularly. Between performing analysis, to sketching out a few ideas, learning about exposure and depth of field, and passing time playing a few levels of Monument Valley, the iPad Air 2 is an ideal device based on my needs.