I bought a CompStock for a 590 because I wasn't sure I wanted to go the pistol grip route. Yes it did work. The recoil reducing portion is a series of springs that physically compress the stock into itself. It shortens by maybe an inch or so when fired. It doesn't feel awkward because everything happens so fast. Instead of your shoulder moving, the stock moves. I know thats a botched description, but it's the best I can do right now.
To be honest, the only reason I opted for the Spec-Ops was for the tacticool factor. As far as I could tell, both had the same recoil reduction. I never did a side by side comparison but nothing stuck in my mind that said one was better than the other. I also have the SpecOpsFolder (previously called the COP Stock). That one works too, but not nearly as well as the full sized stocks. The wire frame tends to dig in a bit with really heavy slugs.
Hope that helps.