A complete system replaces everything downstream of the catalytic converter. Its main effect is acoustic: less restrictive silencers, a deeper tone and a more pronounced-sounding rise in revs. In terms of power, the gain exists but remains modest on a stock engine, because the main restriction in a production engine is upstream - the catalytic converter and downpipe.

The second effect, less heavily marketed and more long-lasting: weight and durability. A stainless steel system does not rust, can still be removed ten years from now and weighs less than the original aluminized-steel exhaust. On a car you intend to keep, it is the part you only install once.