The Z charger has belt slipping problems...I've seen some testimonies on Vortex...not the way to go if you want a s/c..
the only good point about it, is if it breaks, cut the strap and drive home.
The vortech takes a bit longer to install due to the oil lines for cooling. It seems to have a better power output, and is very reliable...but if it breaks, call a tow truck..