We probably have different definitions of "big guy" and "perfect on the plane". I've taken my 12.9 on a few plane trips... far from perfect. When the person in front of me puts their seat back down, there's no room for it... and I'm not anywhere near as big as the guy in the photo.
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That Big Guy is only slightly larger than me. I stand 6 feet tall and weigh in at about 220 lbs. My traveling has been light and only lately (as I really don't like to fly. Having an Airframe and Power Plant license has me a bit too "aware" of mechanical things to enjoy the take off and landing part). But I had no issues at all using the 12.9 inch in flight. But I really can understand how it would be problematic for others.
I am amazed at how "active" some people are on airplanes lately. It's usually a handful of people who just can't sit still for a few hours while the flight occurs. Constantly up and down and getting into the overheads and going to the bathroom and just constant "somethings".
I'm probably one of the most patient people in the world on an airplane because of my knowledge of aircraft and "how things work" and how just one individual can change the way a plane acts in a very short amount of time, just because they won't sit still... Just the Staff on the airplane cause enough adjustment to flight controls. Consider moving a small weight along the axis of your paper airplane and how it affects flight... even the big planes are affected the same way... every time someone moves fore and aft... not to mention moving the weight from... say a window seat to the aisle. It's constant adjustment (mostly noticed and adjusted by computerized systems nowadays... but still...) As an Airplane mechanic I feel almost every move and correction, and see the adjustments made and hear things happen to work that out. so I don't rest well in the air.
I notice when the plane slows even a few MPH when most people wouldn't have a clue. So Basically, like many people, my iPad is there for my distraction mostly... so I feel very compelled to use it as much as possible on board the planes. But I would possibly be inhibited by some situations as some have described here as well if the airline had the configuration too tight to enjoy using the iPad... then even a smaller one might be too much as well.
Like I said before. Bring on the toys! I like them all and would love to have one of everything as far as gadgets are concerned. There's a perfect situation for all of them, and some of them are perfect for almost All situations.