I've had tons of success with pre fertilized potting soils like MG, Schultz, Fertilome, etc. You just have to know how to use them.
An easy strategy I liked to employ was using MG for veg and running all the chemical ferts out of it with plain water feedings (2-3 weeks). Then I would transplant to a non fertilized soil like Pro-Mix for more accurate feedings, since MG does not have an ideal flowering food in its standard mix. With both soils not fertilized it was easy to use a veg or flowering formula with no worries about double dosing.
Good luck
Smokin