This design is most effective because it directly address the user’s need by integrating ergonomics, performance, and functionality.
Some important parts are following :

Guard / Collar
Protective barrier between the blade and the hand.

Contoured Surface
Handle for the user to hold while carving, with repeated indentations that allow fingers to rest naturally for ergonomic stability.

Handle Thickness (3cm diameter)
Physical foundation of the grip, calibrated to average hand size for secure and comfortable holding.

Small Hole (Guard / Collar)
Entry point for the screw that secures and allows easy replacement of blades for different carving tasks.

Ergonomically, the contoured handle aligns with the natural shape of the hand, reducing fatigue and discomfort. This also enhances performance by giving the user greater control and precision during carving.
In terms of functionality, the blade replacement system allows the tool to adapt to different tasks, making it more versatile and efficient for users. Specifically, the user has mentioned that some carving tools have wrong size ; this addresses it by combining finger-fit hand grip and different blade sizes (small to big).
Even the small details like ‘name sign’ and ‘AR coating’ also help the user recognizes the carving tool among others and wash it easily.
Overall, the design is user-centered, as each feature is not just added, but specifically improves how safely, comfortably, and effectively the user can perform the task.