Took it for a thorough road test today with good mix of around town and open highway driving. I'll preface this feedback with as we all know this is a Jeep Wrangler, so it's never going to be quiet to the levels of a luxury sedan by any means.
That said, I'm giving the "Sound Assassin" stuff two very big thumbs up! There is definitely a very noticeable difference. Road noise is clearly reduced and the floor feels more solid or substantive (for lack of more precise descriptive terms) and that tinny vibration like feel is totally gone. The Butyl material also provides thermal resistance, so the cab doesn't heat up as much. It felt like my AC (on auto setting) wasn't working as hard to keep things cool. You still of course get the wind noise from the flat windshield dynamics and the lack of roof insulation (I have SOT roof), but the overall cabin noise level is much better. I also have the Hothead Liner for the SOT that I installed weeks ago, so have a little extra sound insulation to the roof anyway. Most importantly, that awesome 392 growl and sweet exhaust note still comes through!
Also was my first chance to test audio difference after swapping out the front speakers with the Infinity Reference set I posted a couple days back. Again, definite and noticeable improvement. With the stock speakers and audio distribution set to "center" I always felt the rears were dominant and sound was coming from behind. Now it truly feels centered and overall sound quality is a little better. Definitely worth the $50 expense and 5 minute install. That coupled with the overall decreased road noise from the floor sound dampener makes the audio experience quite a bit better (again, it's still Jeep Wrangler though, so don't set expectations too high).
Overall I would definitely recommend the Sound Assassin.
My $.02 for whatever it's worth. Hope that's helpful.