When all else fails go to the mfr website. The tip is actually 1.9mm in size, or about 5.4 pixels. Here is their FAQ page for it:
http://www.adonit.net/support/pixel/
According to them the tip is designed to be softer than the screen glass and to last for about 100km (62 miles) writing distance. Of course if there is any dust on the tip or screen, THAT dust might contain particles HARDER than the glass. It is usually these hard dust particles that cause scratches.