Hey there snuggles,
Really great question. I worked for a couple of years at a mushroom growing factory, and I can say this about mushroom compost;
Add a bag of perlite, and a small bag of good starter soil.
Here is what the product is;
1. Piles of cattle manure left outside to first ferment, and man it does get hot and stinky. We used large tractors to scoop it up, and put it with a big pile of loamy earth, then we mixed it up with shredded straw and styrofoam balls. The styrofoam balls were the same size as perlite. Basically it is the same stuff.
We blended this all real well, and left it to mature and leech. In the end process we would add extra dirt and straw and then run it all through a tumbler that seperated out the rocks and other unwanted matter. Man you wouldn't believe what all could handle the harsh stuff, and weeds even grew like crazy.
If the PH was correct we would fill large flats with it, and put it into a large barn that was kept in almost total darkness. Mushroom spores were added and then we just watched the temps. the humidity was self regulating as it was hot and humid inside the barns. auto sprinklers would run and if you weren't watchfull the entire barn could go up in flames.
After a awhile though the soil was removed, and a fresh batch was then brought in.
The old stuff was blended with ground up shroom roots, and smashed up shrooms damaged in all the processing. A big pile of this would accumulate and would be then bagged and sold to buyers everywhere for their gardens.
It is a good compost but tricky to use as it can and does burn the snot out of sensitive plants. It is however an excellant product to further enrich your potting soil, but I would use it as an enrichment only.
Good Luck Bro.
smoke in peace
KingKahuuna