It's decent stuff. You'll need Cal-Mag. Or just skip that like I do nowadays and add Dolomite lime, mix, water and let it set for 2-3 days before planting in it. No need for Calmag then.
As far as nutrients go it's important to use a food with a good micro blend. Most off the shelf nutes come with a nice ratio but it's something to consider.
A good perk with promix is that it absorbs and wicks up water really well. You can easily lazy man water it by just having your pots inside of cat liter boxes or watering trays. Then pour water or plantfood in there. That's if you're in a hurry.