I can't attest or detest to the productivity of MG soil / nutes. What I can tell you is I previously had started some plants in MG soil, and a couple weeks later they stayed pretty stunted, and some appeared to suffer from nute burn. Bought some organic soil, transplanted, and they recovered. It was my first grow and I can't say whether or not the MG soil was the cause, or just amateur techniques.
Funny story in correlation to that: recently germinated some NL x Big Bud seeds, realized I only had enough of that organic soil left for three 16oz beer pong cups and the roads were covered in snow so I couldn't drive down to get more organic soil. Didn't want to let the seeds sit in paper towel any longer as the taproots were already about 3/8" long, so I said fuck it and found the leftover MG soil (almost a full bag) and put four seeds in it. That was 2 days ago. As of yesterday, 4/4 planted in MG soil had sprouted, while 3/3 in organic had not. This morning one of the organic soil seedlings sprouted, and the other two have not. Granted I assume this was caused due to the MG soil being much older and more dried out, so when broken up and watered, it formed a less dense and softer soil for the seed to push through than the organic soil which is pretty dense in comparison. I just found it funny that a soil commonly regarded as inferior had produced the best short-term results. Will be transplanting into FF Ocean Forest next week.