I did this tonight and the sound is much deeper under 4,000 RPM. Noticeably better... and louder. Downshifts make a really nice, deep growl and far more suitable to the car.
A bit of drone in 7th on the highway but not bad. The cold start and initial drive off is WAY louder... like much louder
Love it and it's free. I would have no need to change the exist with this mod unless someone wanted stupid, annoying loud.