grdwalker: how does the VFNZ firmware differ to other standards?
Looking at the firmware Intratech posted on XDA, the main firmware (kernel and baseband) is identical to the generic XEU. The only difference is the CSC (carrier-specific customisations) file.
I don't know exactly what changes VNZ have made in the CSC file. There may be a custom boot screen, new apps, removed apps, and/or restrictions made to the phone settings. It's hard to say without a thorough examination.
The only thing that should be of any major concern with the VNZ firmware is how long it takes to get updated when a new round of firmware updates comes out. The XEU firmware is generally one of the first to get an update, and carrier-specific versions come out after that. It's a good sign that VNZ uses the same kernel/baseband as XEU, as this might help speed up firmware updates.