I have a volant on my 04 SCREW combined with an edge and a Banks cat back. With this combination I saw a significant increase in response and power as well as improved fuel economy.....All depending on how nice I am on the skinny pedal that is. .

I have had no problem with my volant. My only complaint is vibration. I have a vibration from it, a drone under load on the bottom end. It has a vibe for a short RPM range and then it is gone. There are several posts on here about this problem.

Hope that helps.
Meat

 

I also noticed the vibration, it will do it under idle once in a while, but if I rev it a little bit it's fine.