Performance will be dragged down at the low rev and cold engine, also due to the nature of SS, the manifold might become loose due to extreme temp changes.
Has your existing banana cracked? If so, just ask the garage to arrange for wielding laa, it is a lot cheaper than getting a SS manifold for the 20vt, this is not a performance upgrade kit as it is not an equal length exhaust manifold like the 16vt ones. You probably saves 1 or 2 kg but no much more than that.
