Miracle Grow Cactus Soil: NOT FOR USE IN POTS? Why not, and can I still use it anyway?

I make my own mix for my "trichs" I sift regular potting soil add course sand, coconut replacement for peat moss called "coir", and perlite. I use the soil and coir in equal amounts, about half the amount of sand, and 50% perlite. I've used the miracle grow but I sifted it and added more perlite to it and it was fine but the cost was more than I liked in the amounts I needed.