Difference between assigning function to props, with arrow function and without

I don’t understand what is the difference between assigning my handleButton method to the props with and without the arrow function. In React Developer Tools I see only this statement func: f func() {} and func2: f () {}, can you explain me the difference?

Code:

<MathButton
    operator="-"
    number={10}
    func={() => {
        this.handleButton;
    }}
    func2={this.handleButton}
></MathButton>