I have the Kenu Airframe as well, first the standard and now the + version to accommodate my iPhone 6+. I wrote up my experiences with it here as well as a photo:
http://e84.xbimmers.com/forums/showt...php?p=16146280
In short, they have functioned well, and I have yet to find a better solution. That said, they aren't *perfect*--the fit is a little kludgy because the knob on the vent itself is a little bit in the way. It absolutely works, but could be a small bit better.
It holds the phone solidly, and it's adjustability can't be beat. Also, when empty, it has a very small footprint, and the new + version (which also works with normal size iPhone 6) is solid black, so its very unobtrusive and classy.
I am a huge fan of Pro-Clip too, but with BMWs, they just don't put the phone in the position I want--this mostly has to do with the position of the vents relative to the iDrive display. Either the phone blocks the screen or I have to position the phone further away than I'd like.