[Spinnaker]

If everything that I have read and if I understand it correctly, Z-Max works by introducing zinc compounds into the oil. These are anti-wear additives. The oil companies reduced these compounds in their oils because they can ruin catalytic converters if they coat the platinum mesh in the converters.
So the choice is to help protect the engine and risk ruining the expensive catalytic converters, or use a high quality oil and change it regularly.
If you live somewhere that doesn't have emissions testing requirements, this may not concern you.