There's a computer lab at my school with Cintiq 21ux's.
(The school does not provide pens, relying on students to buy them themselves.)
I decided to use the Intuos3 classic pen that I use with my own tablet. It seems to work all right. But there's some lag.
Is there any real difference between the performance of this Intuos3 pen, and the performance of the actual Cintiq pen on the 21ux?
I overheard someone saying they thought the Cintiq pen was more "calibrated" to the machine it was designed for, therefore it had less cursor lag. (But it seemed like they didn't really know what they were talking about.)
If I had an actual cintiq pen, I would test the theory myself, but nobody seems to have one yet because the lab is brand new.