LogicalOne
The main difference in Nitrogen, is the pressure change in Nitrogen is less effected by heat and altitude as compared to air. The head being pressurized was ideally supposed to increase rigidity and the trampoline effect of the head. Zevo had a head called the "Kompressor" that pre-loaded the head with something like 60,000 PSI by using a zytel cable that internally attached the crown to the sole with a special fitting that was tightened at the factory.
The Powerbuilt head has a clean look IMO.