Promix is excellent, I don't use anything else but I usually like to add a bit of sand and perlite as well to aid in drainage. I never go without mychorrhiza in my soil, it does help the root system a lot and I noticed a big difference in my plants health and rate of growth when I started to add it to the soil. I usually like to add the mychorrhiza separately using Fox Farm Starter Fertilizer. That way if the soil you got was stored outside and may have been contaminated you can sterilize it and THEN add the mychorrhiza... also a lot of soil companies charge way too much for the added fungus so I tend to save a bit of cash that way and just get the traditional promix.