The surface of the Stone Hammer that touches the Letter bits during the seed phrase stamping process is wider than the Claw Hammer, thereby minimizing missed hits.
The stone hammer is also heavier, so the pressure when hitting can be more optimal than when using a Claw Hammer.

When I practice backing up seed phrases, washers made from stainless steel can be harder than those made from galvanized iron plates (the thickness of the material also affects), so you need to hit harder so the stamping results can be clearer.