I am also very impressed with the KL Null SMZ holster because it seems to be excellent for under the shirt wear, especially if the shirt is not transparent, and not too thin.
Again, the belt clip can be attached to the waist band of men's undershorts, or the horizontal component of a woman's bra, according to the fitting instructions.
There are so many times when a shirt is best tucked in. This holster is perfect for those occasions.
I'll probably carry the R9S empty for a while, and get accustomed to a pistol pointing straight up, near the armpit.
Bill