Yeah, the music rack for the KN5 is adjustable in height. That's because when the display angle is all the way up, you need the added height on the music rack in order to turn pages - else they hit the display.
I don't know what those 2 vertical slots between the top & bottom holes are. They have a piece of plastic in them. Not sure - the manual doesn't say anything about this. And the picture of the music rack in the manual (page 8), looks a little different than my rack.
And yes, it's flimsy in construction.