ingredients to fertilizers are ubiquitous.. they are commodities. this means, except for esoteric non-specific organic products with widely varying contents, there are no higher or lower tier quality ingredients. Magnesium Sulfate is always magnesium sulfate. the atomic structure does not change if the product costs more or has a neat-o cartoon graphic resembling some sugary cereal marketing :P "A rose is a rose..."
the same factors that go into robost growth relative to genetics apply to any fertilizer used...
so if it is overpriced... definitelry bullshit. if they have 20 products when you only need 2 or 3 to safely mix things up and avoid precipitates etc, then it is definitely bullshit. predatory business practices aimed at rubes. it is incredibly effective especially with any hobbyist crowd.
proper ratios and concentration of fertlizers, pH, temperatures, RH%, co2 levels dictate growth rate. Genetics dictates potential -- your ceiling. not brand names... Soil is more complicated but still has to average out in similar ways in regard to fertilizer that enters the plant over 4 months. it just has other steps inbetween application and plant-available for some stuff, like N. if you accounted for all those differences, youd finde that the amoutn of fertilizer taking in correlates to same growth, but probably more time to get there. (law of conservation of mass.. the fertilizer is the "ibeams and bolts" for cellular reproduction and other various processes that maintain the plant - can't rely on spontaneous manifestation as pastuer proved with his experiements)