XD does not stand for extra distance. Rather, the XD is another great disc in the Innova series of putters. While it is not made for distance, it is your go-to putter on a long approach or long putts. Some actually use the putter as their distance disc when nothing else is available. 
 
Halo Nexus is the Halo version of Innova's Nexus plastic. It's a tacky and firm plastic with a beautiful Halo effect.