Mouth calls seldom work the same from person to person. Everyone has a slight different shaped palate, difference in how they apply tongue pressure, air volume, and skill. There are calls (both elk and turkey) that I've seen folks rave about that I think suck.
This. Rocky Mountain Hunting Calls has a chart going by latex thickness/calling difficulty and palate shape. Figures why I love the Blue and Yellow and struggled with Green and a couple others; I have a flat palate and the rounded plastic tops screw up positioning.