Tom Threepersons was a legendary figure in law enforcement, serving at various times with the Canadian Northwest Mounted Police, police departments in San Antonio and El Paso, and as a mounted US Customs Inspector. In about 1920 Threepersons had a holster made to his specifications by "Tio Sam", founder of S.D. Myres Saddlery Company. Unlike most holsters of that time period, the Threepersons design rode considerably higher on the belt, featured a modest butt-forward cant, and fully exposed everything on the revolver behind the cylinder, with a completely exposed trigger guard. The original was made for Tom's .45 caliber 5-1/2" Colt Single Action Army revolver.
The emphasis of this design was obviously on accessibility, the ease with which the revolver could be gripped and drawn from the holster. Additionally, the higher ride provided better comfort for mounted use (either horseback or in vehicles). Concealment was not a prominent factor in this design.
That said, the Threepersons' style holster rides quite closely to the body and fairly high on the belt. With a reasonable cover garment these are not difficult to keep concealed under most conditions.
If concealment were my primary goal the Threepersons' style is not one I would select. From a purely aesthetic standpoint there are few holsters that are more appealing to the eye.