I haven't used it, so can't speak from experience, but everything I read mostly just says to stay away from anything that says potting MIX, and try to avoid the stuff that says it provides "x weeks of nutrients". Reasoning being that you want to control the nutrients going into your plants, not some time release soil additive. Also get something sterilized, and if possible something that has a PH of 6.5. PH can be adjusted by mixing the soil with limestone based products or acidics like peat, figure this out in the mix, before you plant in it. I believe miraclegro is mostly nutrient release products (though I could be wrong).
My limited experience seems to show that you can approach this kinda two ways. You can work with and learn about the soil and additives, and give plants a perfect growing medium, and just do the mobile macro nuts as needed. Or you can go primarily with inert mediums (perlite, coco, etc), and add all the things the plants needs through additives when watering. Both have advantages and disadvantages, most of them are fairly apparent.