I've carried a full size Glock in the Smart Carry for several years, as well as a compact Glock, a baby Glock, a Gov't 1911 and S&W snubbies. The full size Glock and the 1911 are not all that comfortable, to say the least. The baby Glock and snubbies are great, and while I had a Kahr K40 for a while, I don't recall carrying it in the Smart Carry. I think it would have been perfect, due its flatness and length. Currently, I carry a Glock 17 this way, as my job requires a tucked in shirt and khakis (or nicer), and I've not yet purchased a Glock 30.
My recommendation if you want to use Smart Carry is a Glock/Kahr/XD compact or smaller, a double action revolver, or something else of similar size with a heavy trigger pull. This is due to the way you have to draw. While the trigger literally cannot be reached from outside the holster, your hand is at a funny angle for the draw, with the pants and belt pushing in on the drawing hand.