I remember that Krita maintains a list of supported tablets. Most of them are
so called "pen tablets". You can try to find such a list on Krita's website.
As for "LCD tablets", I have tried the following models of ThinkPad. All work
fine with entirely free/libre software. The models include X41t, X60t, X61t,
X200t, X201t, X220t, X230t, Helix (1st gen.) and S1 Yoga (1st gen.). The pen
tablets of W700 and W701 also works fine. Any newer ThinkPad has Boot Guard
so I won't consider them at all.
You asked why iPad Pro is much cheaper than professional "LCD tablets" like
Wacom's Cintiq series. The answer is that the precision difference between
them is too big. iPad Pro's "pencil" cannot be classified as a digitizer
because of its poor precision.
