Most people either use them an kneeboards or use a ram-style mount to attach them to the yoke.
My best experience was with the iPhone 4, iPad mini and MacBook Air. Phone was small enough to be unobtrusive, iPad mini was good enough for reading, MBA was just about perfect for casual computing (though I would love a SD or micro-SD slot). My uses were Django programming & photography.
The iPhone 6 & 7 are awkwardly sized: too large to be unobtrusive too small for easy reading.
The mini, in comparison, is much like a Kindle for reading books (that is it's comfortable to read, especially the retina displays), and I can read just about any web site without special handling when in portrait mode.
I've bought 3, and the only reason I haven't bought more is because they still work perfectly.
I bought the original iPad and the iPad 2 and never found a use for them, so when I needed a new iPad for work I went with the cheapest one. I actually found with the Mini form-factor I started using the thing, and now the 16 GB storage makes it a massive pain in the ass because the features that make the iOS ecosystem really seamless (iCloud) don't work with 16 GB.
Now I'm left wondering if I should get the mini 4 on this rumor...
I am a bit worried about Apple's desire to remove the bezel since that will cause some problem and iBooks likes to flip a lot of pages if your thumb strays.
1)  the iPad pro is just a no go because of its size, and the iPad 9.7 is too big for a lot of children and some adults. Remember, a lot of activities are hold it up with one hand for long periods of time while tapping with the other.
I think that is where iPad is heading. Some argue Apple is obsess with thinness, personally I think both iPhone and especially the iPad has a long way to go before it is Too Thin.
Its the Mac Pro argument, people aren't buying it because it hasn't been updated.
Is it based on guess work? Close reading of public statements and financials? An ex-employee with an axe to grind? No clue.
Now it looks like the 11" MBA is being phased out, and the mini also. My hope is that the bezel on the 13" laptops will continue to shrink so that the footprint ends up about the same as the old 11", and then maybe I can upgrade to a 13" laptop and a full-sized iPad. Until then, I'm in a holding pattern.
My iPhone 7 Plus is great, but my iPad Mini with the Zagg keyboard case is fabulous as a portable device for writing, remote access, etc. I'll really be disappointed if Apple cancel it.
The iPad Mini size is perfect for watching video in bed in the evening/morning for me. iPhone Plus could probably be doable, but I don't want to carry that huge thing in my pocket all day.
It's also convenient to use for the DJI Go app for my drone, which absolutely demolishes any device battery. It's light enough so your arms won't get tired, and it spares my phone's battery.
iphone 6 9.4 sq inches.
iphone 6 plus 12.9 sq inches.
ipad mini 29.6 square inches
Have...have you ever used the two? I own a bigger iPhone and an iPad Mini. If you put one on top of the other the size is significant. Yes the mini isn't, say, twice the size but it's not insignificant either.
This makes the iPad Mini not really "pocketable" but the iPhone still is.