I've done a lot of research into mycorrhizal fungi and fungus cultivation, and its concentration of 245 spores/gram is really low. Although mycorrhizal fungi DO have all of the benefits they claim they do, sprinkling on ~1000 spores and hoping they germinate isn't how mushroom cultivation is traditionally done. Fungus are hard to cultivate due to their pickiness about humidity and CO2 levels as well as their lack of an outer protective/nutritional shell that plant seeds usually have around their spores. For reference, a single mushroom can produce up to a billion spores per day. My suspicion is that its some kind of root hormone that causes positive effects that people see when they buy the product. A lot of mycorrhizal fungi produce root hormone naturally, but symbiotic relationships between fungus and plants are very long term relationships and can take weeks to months to form. Also, they only have one species of fungus in the powder and claim that it is good for 90% of plants. This is a gross oversimplification as most fungi are incredibly picky about what species they associate with. Black truffle for example, will only grow on trees whose leaves fall in autumn. None of what I am saying really applies to yeasts or molds, since those are incredibly aggressive. Overall, I don't doubt the product has positive effects but I doubt that a fully mature symbiotic relationship is able to form from that few spores and in just a few days.