Was Jack's Fertilizer formerly known as Peters? Many years ago, Peters 10-50-10 was what I ran for bloom consistently, in hydro and soilless /soil.
It was the only readily available brand that had additional Mag. It was even less expensive than MirGro here.
I never had an issue with Magnesium deficiency until Peters was no longer available.
When I switched to the expensive, over hyped, liquid brands at the hydro store, Mag deficiency was almost always an issue.
Good stuff, thanks for the info, I'll be looking into Jacks for sure.