I have added spores to my garden for a few years, & the results have been excellent. Not only have the plants thrived, the network spread through the lawn to a further extent every year, & the grass in that zone looks much healthier than the rest of the lawn. Mostly I sprinkle a bit in with each seed or row — it does the work from that point on.
Trees have shown the same pattern — we had a large, older tree go down, one which had quite a bit of fungus growing around it, & the trees planted near the old site did well while new trees on the other side of the yard did not, even with significant, regular watering.