Flourish comp is good for low light planted tanks. It's good for water column feeders like anubias, stem plants, and java fern. Root tabs for root feeders like Swords and Crypts.
When you step up to moderate or high light, that's when flourish comp isn't that comprehensive as its name implies. You'll need a good regimen of macros (NPK) and micros -- (i.e. EI or PPS-Pro dosing) -- and carbon source like co2 or glut.