I install a megan with resonator test pipe on my ap2 2005 s2000 (cheap, only 99$ on ebay). First, its perfect fit but you will need to find the good spring with bolt kit (the s2000 oem kit dont fit good and no replacement kit included). The pro: as it came with resonator, it is a good cop fool for a cat removal and it resolve exaust rattle (remember that i have a very conservative and smooth sound apexi ws2 not free flow exaust). Patience for performance feeling upgrade, it take me many miles (around 800 miles to pcm to adapt and dont miss to reset your pc by remove negative cable to battery to realise real upgrade). Rpm snap faster and car speed up faster on part throttle, full throttle is not a so big improvement but it is real (seem to me around 5 hp on dyno butt!!) and you need to like the racing fuel odor feeling to fully appreciate the upgrade!!