Mine works well, but i find like flourish excel it often leaves a slimey coat on the surface of the tank. This is likely just too much fert that is being consumed or maybe it is one nutrient in excess. My trace element states it has balanced proportions. The slime can easily be removed through siphoning the surface of the water or just doing a water change to break it up and dissolve it, it is a pain though as it cuts down on light levels. The advantages exceed the disadvantages though and is especially economic compared to commerical ferts.
You want 0.1 ppm of iron so you could invest in a kit. Any more or any less the authors of PMDD at thekrib state has equally detrimental effects. Just like any nutrient, it should be just right.
My mix is a combination of macro nutrients N-P-K and micro nutrients (trace elements) but you could have them separate the N, P, and K, as well as the trace elements. Every setup will have different requirements for the nutrients but I don't know how you're supposed to know which are more or less required for certain plants and setups.