Rainy day today, so I decided to put on the isolation kit.
Real easy to install - about 1/2 hour.
I didn't do any mowing with it afterward, but took it outside and fired it up. As I said before, mine wasn't real bad, but quite noticeable. Ran it up to PTO speed, and I could actually hear the hum of the mower deck which I couldn't before. I still hear a little bit through the ROPS, but not nearly as bad. Of course the real test will be with it under load, but so far it cut the noise in half for me.
Like Fred_G says - I hope to be able to hear the grass being cut now!