a kenne bell twin screw supercharger is able to make more boost and are much more efficient than any roots style eaton will ever be. I've never personally seen one on a mustage, but its a better supercharger than the new cobras come with. It's more like the supercharger thats on the new gt40.

The only cars that has ever had a twin screw supercharger from the factory are the new gt40, the new mercedes supercar thing and the mazda millenia S - which is a crazy efficient miller cycle engine. Almost all supercharged cars use a eaton roots blower.
Jackson racing is simply an eaton supercharger kit.

I have a supercharger from a mazda millenia that I'm planning on installing on my car...

a twinscrew without a intercooler can be better than a roots with an intercooler. You can imagine how good a intercooled twinscrew will be!

-Jeff