My highly untechnical reply would be that the improved design incorporating the shiny steel belt guard prevents a cam belt vibration which could cause a premature cam belt failure.
The new updated water pump also has an upgraded bearing and seal.
Possibly more improvements.
If you have no experience in adjusting the cam belt I suggest you spend more money on the new tool from Arnnworx to adjust the belts.
920Xv6 Timing Belt Tensioning Tool - Version 6.1 920X Timing Belt Tension Tool [920Xv6.1] - $160.00 : ArnnWorx Specialty Tools
J_AZ
EDIT again..
As long as you are doing the belts, rollers and water pump, you should also reseal the front of the engine. Replace the seals and other parts WYAIT: Example
http://www.pelicanparts.com/catalog/SuperCat/0991/POR_0991_ENGREB_pg1.htm#item4
More?
J_AZ