The only thing that comes to mind is that how will you protect the glass from scratches
The Z Ultra is able to take input from ordinary pencil but to do so, make it easier to scratch. In term of sensitivity it is near perfect imho, only lacking pressure level recognition.
The way for me to do it was, to buy any additional screen protector (i.e. the Nillkin one will suffice) and use some soft material for a pen, which in my case is an ordinary cheap chopsticks, shaved like a pencil and soaked with water. It works perfectly. Or like some other, they bought the Galaxy C Pen for it. Both shouldn't be able to scratch the screen.
Love to Mod, Love to Experiment
Sony Ericsson K700i
SE Xperia X10 Mini Pro
SE Xperia Ray
Motorola RAZR Maxx
Xperia Z Ultra