I used that stuff when I first started, before I knew what excel was, and hadn't yet built a DIY CO2 rig. My plants seemed to respond to it, when used as directed. But then again I was a newb, so I'm not sure we can trust my observations at that time. If pressed however, I'd give it a shot again... think I even have some extra laying around in a tackle box somewhere.
Steve - 33g reef and a 180g planted in need of a re-scape.