If you're driving a JDM zed you will hear a difference - if its a UK you will hear a slight tonal difference over 3.5/4k revs. Then again supposedly you can put the same exhaust on identical cars and it will sound different.
Milltek only make resonated exhausts for the zed.
You should also find a difference in low/mid range torque and I definately had an improved throttle response - which to fully exploit requires a wee 'flash' next year
Take it you have seen this?