4 into 1 exhaust heders

Hello,

I wanted to know what was the list's experience with 4 into 1 exhaust
headers.
What does that change to the car?
I need to change the mufler, and I am planning to get rid of the catalytic
converter at the same time, and I was thinking, while I am in this
vincinity, that I could change the headers....
What do you think I should do?

Thanks, cyrille