Had them on my GT6 from the PO and they were new when I bought the car.
Monza system = VERY loud, in fact so loud that it was hard to hear normal conversation at highway speeed (forced me to wear foam ear plugs on trips). And remember, the stock GT6 exhaust system is relatively quiet, in fact it's practically silent compared to the Monza system.
Also, RUST. Mine rusted within a year. The Monza attracted rust like a magnet. In all deference, tho', it's fairly humid here in the summer. YMMV regarding the rust.
IMHO, it's a cheap, loud system. Go with stainless steel from a reputable vendor like SpitBits (Falcon, etc.), you'll be glad you did.