I'm using the 10.5" Smart Keyboard right now to type this (albeit with a 9.7" Pro, of course, until next week).
Doesn't seem upgraded at all in terms of functioning, key travel, clicky-ness, etc (I have owned and used both the 12.9 and the 9.7 SKs in the past.
The size of course is different. And you know what, these devils are almost always right. I do think that -- at least for my hands -- the extra centimetre you get going from the 9.7 SK to the 10.5 SK begins to make a difference. On this, the 10.5, my fingers fly confidently, and I can see myself getting relatively used to it in the short term. The 9.7 always felt a little on the wrong side of the magic line, for me.