I asked ServInt to install this onto my server last night, and for me, the results are amazing. I had APC caching implemented, which I have now removed entirely with zero effect to page delivery.
Prior to this, with caching and server caching, a lot of style tweaks and such to remove http requests, thread pages often struggled to get close to 90 on the Google pagespeed test... now they score 94 + / - depending on page. Pretty much above 90 regardless of the page across all my sites.
I have disabled my APC backend and frontend caching, as it made no difference to page loading with this installed.
ServInt did say that their experience installing this for customers has been hit and miss. Some it has worked truly well for, others it has caused their server to perform worse.
Before you ask... you're unlikely to get this installed on shared hosting, not unless the host has installed it for everyone.
Have you used it? What is your experience with it?