I carry IWB for two reasons. It conceals better and I think it aids retention. If I do OWB carry, I usually use a Safariland ALS holster. they're more bulky, but have a built in retention device that's safe to use and doesn't impede draw speed. Pancake leather holsters and kydex like Raven Concealment builds can be pretty easy to conceal, but most people would have to buy extra long shirts to prevent "peeking" from underneath.