I have both the Magnaflow exhaust and the Dual Needswings on my NA. One thing you will notice is the sound, its a lot louder. If that's what you are after then you will be a happy camper. I like loud. As for performance strictly from a "feel" point of view maybe a tad bit quicker? But if you were expecting a lot of extra horses? Rob is better to answer your questions as to the actual difference all I know is it sure looks and sounds cool. And no there is no ill affect on the engine.
Pat