MK III Golf GTI Manifold Query???

[Big Ashy]

Wonder if any of you VW owners could answer what I think is a straight forward question. Recently bought a 2.0 GTI for The Track, did the usual, stripped it to its bare bones, fitted a decat pipe and K & N Cone filter, was going to swap the standard cast exhaust manifold for a free flow but was advised not to as it can reduce performance?

Alledgedly, and I quote, "The head needs a lot of porting work ect carried out on it before the benefits of a after market manifold are felt, your`e wasting your money".

Goes against the grain in my book, can anyone advise whether this is correct or a load of boks.

Any other cheap bolt on performance recommendations greatly appreciated, thanks in advance, Ade.