I use a woodworkers clamp bolted to my shop table after using whatever glue I choose. Don't clamp it to the point of deforming the leather but I feel it gives the glue a better, more consistent set. It's big enough to clamp almost every holster I make and I use two large boards for anything larger.
I have used it to press two pieces of 6/7oz leather into a welt the thickness of one as well, as a flint holder for a sheath as well. Handy tool but be careful of pressure applied.