I agree with the above. I've had mine on since yesterday, and now, at idle and revving from idle, it sounds like a freaking BEAST inside combined with my exhaust. Definitely not much more noise or vibration when you're cruising, so i'm hapy about that. I don't notice _quite_ as much of a difference upshifting, however I have an ACT clutch kit in and that did a HUGE amount towards my shift feel already.... That being said, where this makes the biggest difference for me is downshifts. When I downshift hard it's just solid. no more engine bounce... It's fantastic.
To sum up: The whole engine feels a bit more responsive and tight. Upshifts definitely feel nicer to engage when i shift hard from say 5500+ rpm. Downshifts feel excellent all the time. Noise at idle is louder and vibration more present, but sounds great and doens't add too much noise at cruising speeds.
Definitely a great upgrade for $80. I can't comment on how much noise would be present in the cabin coming from stock as my exhaust and intake probably make a bigger difference to internal noise, but I woudl say if you're on this forum, you're probably a bit of a 'driver' anyway so most people looking to mod probably wont mind so much.