The M90 is the supercharger fitted to the supercoupe.
There are different generations though, so be aware. The gen3 M90's have ported inlets, so just like the C/I head, they breath better. Made a few more HP even though the rev rate dropped a little.
In my humble opinion the M90 is a great answer. The highest priority on Eaton/Magnuson's list was reliability. They are good for 150,000 no sweat.
They are produced as OEM equipment, and are fitted by manufacturers to a wide range of vehicles. Here in Australia, they were fitted to recent model Holdens (GM), but are also fitted to Jags and Hummers.
It has a big brother, the M112. I have read that because of it's size, it is most effective at a higher rev range. So the M90 is about our optimum choice.
If you can't tell, I am sold on them. I have one, it has been part of my plan for a while.
Dan