I have one on my 1999 C5.
The Good:
- Awesome power - expect a safe intercooled setup to increase your rwhp by 50-60% at around 8-10psi, so you should see ~600 hp.
- Power all the time - I ran N20 before the Procharger, I like the power always on tap.
- endless smile on your face while driving
The Bad:
- Have it installed and tuned by an experienced professional, I think this is very important
- I hope ATI improved their brackets/kits. The C5 kits were poor and much of the R&D and improvements were required and made by the tuners.
- the greater the power, the sooner you will find the weak points and break them -- clutch, outputshafts, rear, etc.
- much of the drivetrain warranty gone - no big deal to me, others it is
- go thru tires more now - my driving habits
- you need to change the oil in the Supercharger - no oil feed like Vortech
- you will not get back what you spend on it if you sell it (unless you find the right buyer), lucky to see 25% in my opinion. It's not a good financial investment, just an investment in your pleasure/enjoyment.
The Ugly:
- broken belts due to poor ATI design/brackets
- cost of all the other things I chose to do - some required, most just my choice. HP available is a function of $$ you wish to spend: $$=HP
Would I do it again?
Yes (though I might consider an LPE 427 Twin Turbo instead)
This is just my C5 experience, no personal experience on a C6. Get it installed and tuned through a reputable shop who will stand behind their work, and you will be much happier. I learned many things the hard way.