Look at how popular the Galaxy Note is. I don't understand those people, but they love it. And I think the iPhone 6 Plus is actually smaller than a Note.
I wouldn't buy it, can't carry it around - forget cycling.
http://en.wikipedia.org/wiki/Samsung_Galaxy_Note_Edge
151.3 mm (5.96 in) H 82.4 mm (3.24 in) W 8.3 mm (0.33 in) D
vs
iPhone 6 Plus
158.1 mm (6.22 in) H 77.8 mm (3.06 in) W 7.1 mm (0.28 in) D
For reference, I literally cannot use his phone one-handed; I can't hold it and reach all the way across the screen with my thumb. I'm a small dude and he's a big one, and some devices are just designed for the opposite extreme.
I have a friend with the note who actually uses a stylus with it. I don't get it but he really loves that phone.