If the bottom of the car was sealed and flat (like on supercars) then yes it would probably offer down force,
However as shown in the picture below the rear of the diffuser is open so airflow would not be channelled correctly, also by the looks of the brackets these would maybe be too weak if it was to offer any major down force.
I am not saying I don’t like it, I do, I think they look good, and certainly my post was not meant to dishearten or get anyone annoyed I was just being honest that its a shame that they wont offer much or if any down force,
In terms of looks I think they look great, they have a very good finish and it looks like it been professionally installed on the car.
Sorry if it came across in the wrong way it was just a passing comment