are magnaflow exhaust systems any good ?

sorry for all the questions lately , but i just finished my stereo and am really getting into performance . my local stereo installer has a magnaflow exhaust on his grandprix and it sounds really nice . i realize that his car is a 6 cylinder and mine is a 4 which would most likely sound a little different on my car . but i am just wondering how they rank in terms of performance and quality . thanks .