I don't believe this to be correct...the factory mugen exhaust has no power gains...the one from king is the true mugen cat back...totally different products.This is a little different but I would assume that the performance would be comparable to the Mugen Si's exhaust.
"Mugen's Sports Silencer for the new 2006+ Civic Si 4-Door is made from premium grade 304 Stainless Steel. The system produces a deep and mellow tone and features a smaller slash cut tip for the sleeper look. 8whp gains can be expected. System comes complete with all hardware and gaskets required for installation. Also includes the exclusive "Mugen Equipped" metal emblem."