I now have 6 MICs. The original, the razor's edge, and 4 custom made ones that accommodate my Viridian C5L. (2 are intended for a buddy who has the same Weapon and Light). I LOVE THEM! I am wearing mine right now, minus the gun. I am at school. I simply slide it on top of my belt when I don't have my gun on me. It just sits there while I'm in class. I would not suggest using a MIC inside gym shorts. Glock's tend not to hold well inside of gym shorts waistbands (most all waistbands for that matter) because the sides are so flat/smooth as opposed to other weapons with external safeties, decockers, big mag/slide releases.
While I have no experience with the neoprene holsters from above, I would suspect they would do a better job for what you want to do.
In the pic I don't have my original. It is attached to a piece of furniture in my house.