Par4QC The SMT is definitely urethane-filled as well. The SMT 579 is without a doubt the "Justin" irons from Xiamen Jasde, as they make all of the SMT/Sub70/DiamondTour stuff and the designs are identical. They both have a 431 stainless body w/forged 455 Carpenter steel shaft, hollow-body urethane-filled head, toe screw in the end, 100% identical specs, etc.
The only question is, are the Kirklands also based off that same design? Well, according to a recent "insider" who posted on Reddit - that answer is most likely, yes. Albeit, with some slight tweaks (such as the .355 hosel, a tungsten weight insert - which the Justin/SMT irons make no mention of, slightly different loft & offset specs, etc).