When the conditions are right then EM treatments will work wonders. The caveat is that the conditions have to be RIGHT. One portion; pH, soil temp,
water content, nutrient supply, being off can create a non-function situation.
This is why the scientific community seems to have a problem with Effective Micro organisms, it is the lack of easy repeatability.
There are aerobic microbes and there are anaerobic microbes, each needing a different setup to thrive.
May I suggest this paper for reference:
em it is by Dr. Higa and Dr. Parr
Do they work? Yes but conditions must be optimal or near optimal
On my farm, I do not use any of the commercially available EM products and I have excellent results. I do however have great quantities of mycorrhizal fungi, naturally occurring em, and a strong population of both earthworms and red wiggler worms.
In my personal opinion, if you take the time to build really healthy soil, you will find that effective micro organisms abound naturally.
If you don't have or can't build great soil, then I think the addition of activated E.M. products can be of benefit by reducing the time needed for healthy soil building.