We work every class from concealment because that's the way we carry. In the linked article, Mas demonstrates how to draw from various concealed positions of carry. Note that Mas has his hand in a bladed position during the draw stroke. Not all agree on everything, but the core principles are usually in alignment. We teach the draw-stroke with your support side hand flat against your body (for a few good reasons). Also the story notes that Mas is carrying an LCR 9 (revolver in 9mm) and I doubt that it is accurate. Mas, later in the article, states that he carries a 38spcl. Mas and I have had the discussion about pistol rounds being use in a revolver, it's a bad idea for defensive pistol use.