Kneeboards tend to be one of those things where there are a lot of different preferences. Some people like A4-sized, some A5, some the back of a fag packet or writing on their hand. I have an a5-sized folding one which opens up into three sections, with loads of rooms for pens, extra bits of paper, etc etc. I love it for long cross-countries as I've got everything to hand. But those with longer legs than mine would find it gets in the way...there are just a few advantages when flying to being a little shrimp.
Why do I think discussion of this very simple topic could go on and on?