The pipes I've been around work at least as well as advertised. As a matter of fact, most work well enough as to make the mechanical noise of the of the engine and drive train more noticable than the exhaust note. On the down side. They do reduce available power output quite a bit.
This subject has come up here before and now as then I still question the need for noise reduction as critters where I am seem to be used to the noise anyway and pay little attention any more. Because of this they're not worth the money to me but your situation may be different.