We tested our e-cutouts with open headers and then open X-pipe with the E-cutouts just after The X and gained 10 hp on a 425hp vehicle. So there is some performance gain to be had. However, e-cutouts (or any other sound changing exhaust component is an indulgence. I for one have had a blast with them many times. Worth the money the first time I used them in public imo lol!
But you got to consider all the negative comments as well. I can tell you if you decide to give it a go, the Pypes versions are 5 year warranty. We've made them for 10 years now and have really worked out all the kinks. Even have an X-pipe that you can attach them directly to.