Do some of the creators of those super detailed head textures use touch pens or do they just use their mouse?

iawesome uses a trackpad but he mostly uses selection tool combined with brush to get smooth lines.
it depends on what tools youre more well equipped with, if you're better with brush/ pencil and blue etc. go with touch pen.
if you know how to use the pen tool and selection tools then you dont really need a touch pen at all but you're pretty limited.

just a heads up you might need to mess around with a few settings until you get a good configuration for your drawing tablet.