I also would like to find a somewhat quiet aftermarket exhaust and fortunately live in a State that doesn't require emissions testing. You on the other hand have to pass emissions testing. I looked at the Remus Street Legal exhaust then checked the requirements for Japan. The cbr250r is actually 249.4cc and in Japan there are DB requirements but there are NO emissions requirements for anything under 250cc. I bet the remus is quiet but has no catalytic converter. I did find a stainless steel Akrapovic exhaust that is also street legal (a little bit longer and bigger in diameter than the others they offer) and comes with a mid pipe that flares to a larger opening where you can insert their optional catalytic converter. This one seems to be truly street legal for emissions and db levels. Problem is the Akro is expensive $425 muffler and mid pipe plus $88 for the cat (US dollars). I just can't quite justify the price because it looks good.