yep i''ve done this, i brought a magnex as the centre section on my stock exhaust broke with some enthusiastic driving

.... liked the way it sounded but wasn't too taken with the looks..... then the magnex centre section developed a rattle, sold it and got a new reno centre section (up to the rear axel) iir around 200 notes, my back box was ok, and i fitted it for nowt.....
imo the magnex does nothing for performance unless your doing big mods, i think the standard one is fine performance wise, just abit poorly made