Well, allow me to weigh in here, since I'm the guy who developed the first of these things, which Mitch Rosen graciously markets as "The Workman."
In all honesty, I would stay away from Kydex for one of these deep cover rigs simply because it doesn't allow the holster to marry itself against your body and allow a smooth cover like leather does.
The Workman, and my own rig that I call the "Undershirt" are made from slightly thinner leather and tooled to the individual gun.
But it's up to you.