QES version here. Cons...it's loud! Pros...it's loud! In all seriousness, when I'm by myself and certain friends I can care less about the drone. This version drones really loud between 1100-1900rpm. The system itself is very rare, well built, and definitely is an attention grabber. I dont have headers, but I'm aware Unequal Length versions will amplify the sound tremendously. Which I won't mind but the drone will be beyond unbearable.