I'm curious why none of these split designs ever feature a trackball on the right half integrated into the board somehow. There are plenty of FOSS trackball designs, it seems like it would just make sense, especially for ergonomic designs, to have a trackball set up where you don't have to move your hand over to move a cursor. Also I don't understand why they're always missing function keys.
So for just F5, it's as easy to type as %. For, say, Ctrl-Alt-F4, I hit layer, then Ctrl-Alt-4, then layer again.
I grant that someone might make much heavier use of function keys and find this inconvenient. I don't miss them in the slightest.
An integrated trackball might be nice, although I'm not sure where to put it that would be comfortable. I have a trackball to the right of the keyboard, this suits me fine.