Only worked with it one day, but loved it. I must have re-worked a couple dozen of old photos. It made some come alive, and enhanced so it looked like the image I saw when I took the shot.
I even worked a few in Color Efex then opened them in Silver Efex. That made for some wonderful black and whites.
Only thing I would have liked more, is if it had just plain color filters.
The concept of stacking filters is great, no additional work needed, just use and stack as your imagination takes you.