I bought the Shadow 2 Kit for my wife's SPO1 and it runs almost flawlessly. She gets a light strike now and then, but pulling back the trigger and firing always sends the round down range. She also sometimes experiences a failure to extract (trying to clear the chamber of a chambered round), but racking the slide several times usually clears up that issue (also cleaning helps this).
Overall, I like the Shadow 2 better than my Kadet II that I run on my 75 Compact due to the full slide cycling back like the 9mm slide. Much easier to get your hands on. An boy are those polymer mags easier to load as well!