Works pretty well for me! The first time I used AutoGain was on a classical recording because the near placed cembalo mic didn't fit well in the mix. The thing is that I had to increase the volume of that mic more than the mics of the other instruments (strings). So there were a lot of balancing issues between the main stereo mics and the cembalo mic.
I tried using expanders but as I'm not that experienced in using expanders the results were rather frustrating.
So I ended up putting AutoGain on the cembalo track and fed it with the signal of the main M/S-mics. That did the job! The cembalo finally had the same dynamic response as the rest of the instruments.
With this experience in mind I upgraded to the Pro version and am really happy with my decision. I like to feed vocal tracks with a white noise and use the RMS mode with less than 6dB boost/attenuation. And it's nice to have the automation envelope written in my DAW, so I can easily adjust the behaviour afterwards.
I give it a 10/10 because the plugin actually does what the developer promises, because it's very cheap in comparison to the Waves' ones and last but not least because of the frustrating-free copy protection policy :)