The earth is absolutely covered in fungus and fungus spores. I don't think a product manufactured from stabilized reishi mycelium would be anything to worry about.
And is based on cordyceps mushrooms. Which are actual parasitoids of insects. They're the famous "mind-control" mushrooms you see in every nature documentary that features ants in the Amazon
Reishi on the other hand... eats trees.
For some possibly useful context. When wood (lignan) first evolved there was nothing that could break it down. And for possibly thousands of years much of earth became "polluted" by dead trees that couldn't be broken. It was fungi that finally evolved ways to decompose it. They're obviously really good at it at this point, but hopefully that gives you a sense of just how specialized an organism has to be to primarily live off of wood
