I don't have enough data yet to make any outright claims as to what plants really need. That will take a lot more time to discover. However, the literature on heavy metal toxicity on aquatic life is very clear: it's toxic to fish, shrimp, and other organisms including algae. At the suggested fertilization concentrations and dosing, it will result in sublethal harm that will not be externally visible. Only dissection and microscopy will show the true harm to organs and physiology. Tumors, shortened lifespan, reduced size, discoloration and dark spots are some of the visible signs but how do you know it's from heavy metal poisoning or from other causes?
Either of the Flowgrow's have too low Zn in relation to Mn. So at low doses, plants may exhibit Zn deficiency or may negatively respond to the excess iron. Again, its not the absolute concentration but the ratios that matter. I think the person just copied Tropica when coming up with this formula unless European tap water has unnaturally high levels of zinc to begin with. FYI: the toxic threshold for ionic Zn begins at around 4ppb; ionic Cu at 1ppb.
As for suggested dosing, dose only when plants appear to need it. Know your plants because certain plants are very tolerant to heavy metal pollution while others are very sensitive. If all your plants are tolerant, then this will give a false impression as to the safe levels and make you believe you can pollute the water as much as possible with no ill effects. But if many are sensitive, then observing their response will help inform your understanding of nutrient requirements.
Lastly, know your water since it may already contain high concentrations of heavy metals and other nutrients which you should avoid adding. This may ultimately mean you cannot use commercial fertilizers but must mix your own. If your pipes are copper and copper concentrations are high, then it would be unwise to add any more by fertilization. It would also be unwise to do large water changes since this would just add excessive amounts of copper and harm plants and animals.