I've had good success with MG soils, and have learned some intricacies along the way.
The MG pre-ferted soils will support an MJ plant for a month under an HID, say 250W or better. More light = less time without additional ferts. At that point, you probably will need to start adding a grow formula to complete vegging and support stretch. The pre-added ferts will not take you start-to-finish, but you're on the right track to not add anything early on.
Water thoroughly every time you water. People cry "don't water cuz you'll release too many nutes!" Wrongola... You need to water thoroughly to keep the water-nutrient balance right, and to move salts down thru the soil and out of the pot. Letting a pre-ferted soil get dry is a sure formula for burnt plants. Water correctly, and you'll never have to worry about burn or pH in an MG soil. My current pots have been running for 4 months; pH is still dead-on at 6.5.
Finally, MG Organic is good soil too, but you need to add perlite for loft. It's kinda dense right out of the bag.
Good luck. Check my grow link if you want to see what MG can do.