Ergonomically designed date stamps feature a power grip. This means that the operator aligns their fingers in a manner where they work in conjunction with each other to maximize the hand capacity. The shape of the handle affects wrist and arm posture.
An ergonomic design is geared to helping the user perform the task in an easier and safer manner. Repetitive motion that may come with the task at hand, can lead to muscle injuries, and avoiding those is the goal, along with increasing productivity and precision.
Leading researchers in the field of Ergonomics Andris Freivalds, Ph.D. and Seikwon Park, Ph.D., have specifically researched and evaluated the effects of this handle and determined that this handle provides significant improvement when compared to the standard handle. You can read the full report here: Ergonomic Evaluation of the Stamp Handle