Flows are chambered mufflers. AKA, they are not a flow thru design(like all the rest are). There are only a few hp difference between them and Bassani/Borla/Magnaflow, but it is measureable(flows don't flow as well). They seem to put sound quality over performance. Also, they will sell you a "stainless steel kit" that does indeed have ss mufflers but they all have aluminized steel pipes. I have herd stangs with the flowmasters and they do sound good. Again they are more expensive than magnaflow.