I'm going to take a quick stab at this one-

I think it's a brand association problem. The soil might be just fine. Not good, mind you; acceptable.

It's their ferts that are really poor quality and inappropriate for this type of plant. From what I can gather, your chances of ending up with a toxic salt buildup are pretty high with that crap MG peddles.

Since the ferts are so bad, everyone stays away from the soil too.

I personally don't use it either; whay bother, since you can get a big sack of nice organic seaweed compost for an even lower unit price?

This leads to another one of my DON'Ts:

Don't go overboard on the peat moss! Sure, it makes your soil nice and light but it has a pH in the 4-5 range, and after being in the pot for a while, if your plants haven't already died of pH problems (nutrient blockage), they WILL end up with waterlooged roots and be prone to fungus.

DO get really good dirt and mix it with some vermiculite or perlite. Good dirt makes bud taste better!