Free is just about the right price for this one, IMO.
I tried it on a variety of sources: drum bus, kick, snare, overheads, bass, lead guitar, vocal. I couldn't find anything that was improved by adding Stressor, despite a great deal of fiddling with settings. Most things it could do I could do better with Pro-C (the exception being ultra-fast attack times that I almost never use anyway), and at much lower CPU consumption.