I bought one of these for use with my iPad Air. I like to take handwritten notes and using the end of my finger to write with doesn't cut it so I've been reduced to writing with a regular pen on paper then photographing the handwritten pages.
Sadly the new iPad stylus from Evernote is a complete waste of money. As I write or draw on the screen there is a noticeable lag between the tip of the stylus and the line being drawn. The pen connects to the App via bluetooth but the connection drops unpredictable, I am using the latest version of Penultimate which, I think, is the App that this pen is supposed to be optimised for. Finally, I have pretty good handwriting but what comes out of this pen is almost illegible scribble, a kindergartener has better handwriting. Unless there is some bug in the way that this interracts with an iPad Air, which isn't beyond the realm or possibility, I can't recommend this pen to anyone.