I was trying to decide between the 12.9 and 9.7 and LOVED the 12.9. Loved the screen size, the usefulness of split screen, reading textbooks on it for school, and the increased space for note taking. However, there were a couple of very frustrating aspects as well that made me go 9.7.
First, why oh why is there no split keyboard? I use this on the 9.7 to type with the on-screen keyboard. The whole point of it is to be able to still type on the large screen! Then you introduce an almost comically large screen for a tablet, and don't allow split keyboard? But even more confusing is, you CAN split the keyboard but only in zoom view! Huh? I actually don't mind the size of the IPP 12.9 too much, but no split keyboard makes it tough to type when holding the tablet.
Second big one is lack of support for the IPP 12.9 screen resolution and multitasking features even after several months. Gmail was zoomed, Wall St Journal was zoomed, along with several other key apps I use. Kindle app does not yet support split view (along with a number of other apps). Was really looking forward to splitting the screen and taking notes from my digital textbooks. Wish there was a way for Apple to enable split view for all apps without devs needing to implement.
Lastly, and this applies to all iPads, I don't seem to be able to open certain documents linked online through iPad. It always opens them in the browser window. With my laptop, I can open in the browser window or save as a file then open in Office.