endospores within the medium itself, usually the germinated spore is weaker than than the spore itself.
when people do an overnight soak on grains before sterilization they take advantage of this concept.
I started looking at this a few months ago bc it’s the only product line of it’s kind in the space. also I asked a couple buddies that buy in bulk and know the owner.
“it’s a proprietary mycorrhizal blend without trich harzianum”
here’s the educated guess: MGP has nutrients like fulvic, humic, amino acids with beneficial microbes while trich evict is a microbe heavy mix to outcompete predator molds
as for alternatives. my local hydro shop has a few different mycorrhizal blends without trich. they even have a coir thats already innoculated with a compatible set of beneficial microbes. it’ll take a bit of testing but it seems straight forward.