Why shouldn't you run the fmf pipes? That's what I have and it seems to do fine fit me on trails and the gravel pit I ride at.plus I don't have the money for a500 dollar pipe.

The FMF pipes will not do damage to your engine.  I think he is trying to say, If you are a gear head looking for some level of performance, the FMF Fatty pipe is at the bottom of the list.