Only a guess, but my take on it is that they use chelating agents & EDTA to buffer the release of minerals, else they would so into solution when mixed and potentially OD a plant. Also, EDTA-based minerals will buffer the breakdown of lime (scale) in solution to stop them from percipitating out. Its the same reason many 'pro' grade chemical ferts come in 2-4 parts - they are separating the mineral sources so they will not combine and percipitate lime scale. If you try 1-part chem ferts like "EcoGrow" you will end up with a granular 'sand' at the bottom of the bucket; because the minerals naturally combine and bleed off lime elements which cannot dissvolve.
Bottom line to me - and its only an opinion - is that FoxFarm is safe and natural. It will not meet the most stringent ogranic requirements - but its natural and not a frankenstein mix of petro chemicals which do not normally occur in the environment.
And no - the products will not harm microbes. Many people add micro mixes to their ferts, ranging from molasses to micro-concentrates.
Its only an opinion but I trust FoxFarm and do not regard their ferts as being 'chemical' only because they buffer some naturally occuring elements in some of their products.
If you want 100% organic flower boosting then try molasses, bat guano and worm castings. Molasses will be available in minutes, fossilized bat guano (high phos) needs to break down a bit, and worm castings are available faster than bat guano but slower then molasses. If I had to choose between only one of those I'd pick worm castings; Mother Nature's killer source for calcium, nitrogen and trace elements.
Sorry to be so wordy...