I compared Caecilia from PW with the one from KT. Very few glyphs are really changed. The main change is that truetype instructions (hinting) are added to all glyphs. Also kerning tables are added and lookup tables for alternates and ligatures.
I tried the font on my KT, but I like original version more. PW version seems too thick at small font sizes for me. Maybe it is adjusted for different screen resolution. Or it is a matter of habit.