Oh I don’t know, maybe having a loaded Glock 10mm next to my chest isn’t that appealing. The MIC holster is just a little added safety measure for me. By all means go with out.
If the holster is anchored solidly to the bag and the draw side is left open, then it might act like a chest rig.
If the holster is loose and the bag is zipped, you won't be getting that G20 deployed very quickly.
