I presume you are asking the Dual Pixel AF of the original C300. In the Original C300, the DPAF is limited to the centre. So the usability is limited as you are stuck with certain compositions with the subject at the centre. However, if the subject is large in the frame then it works as some part of it can be in focus. You can also lock focus using the DPAF and then recompose. In certain interview situations, where the person is moving or rocking in the chair, the DPAF is of great help. If you are a presenter yourself and are speaking infront of the camera, then the DPAF helps in focusing on yourself.
The dual pixel autofocus also helps in acquiring focus faster (with long telephoto lenses) when I am scanning a landscape for my wildlife subjects. In normal course when a person is moving in an erratic manner, the DPAF helps, but again the DPAF version 1 of C300 ensures that you have to keep the subject in the centre. The C300 II dual pixel auto focus is better than that of the C300 original. And the 1DX II dual pixel auto focus is better than the C300 II.