I have his silencer with an FMF Gnarly head pipe. Great combination. What I like about the HoH pipe is that it is 1/2 the size of the FMF silencer and 1/3rd the weight, as well as tucking under the number plate and not sticking out of the rear as much as the FMF. It is louder (like much) and will require a rejet.
I did not fork over the $$$ for the HoH header pipe, but I am VERY happy with the Gnarly, SO much better than OEM...like different bike.
Just remember it is louder. Not as loud as say a full MX 2 stroke with shorty silencer, but loud.