not a bad idea if you want to avoid the police eyeing you off. Also would be nice to change between a loud car adn a quiet one, could surprise people your driving near too! haha. dunno about the note it'd give out though, be alright on an 8 i'd imagine.
Only one problem I can see. They have been illegal on road cars in NSW for about 40 years. I know this because some friends got pinged by the boys in blue a few years ago for these. I don't think the laws have changed recently either. They sound like crappy lakes pipes.