Appears to be a passive system.
That wing is working on a different principle from Mclaren it seems. It looks like they are looking for more down-force than actually stalling the wing with that device. That pit area in the middle of the wing has a very high pressure, but slow velocity. The fin is adding some velocity to the hole to keep the flow more attached on the back side.
The middle of the wing is the area where the flow is least attached and has lower velocity. As you go out from the center yoward the end plates the velocity and upwash increase. I think this solution is to increase the upwash in the center and make the wing more effective over it's span at creating down force.
On the flip side it could be detaching the flow from the center by pushing it down away from the surface of the wing. This will only stall the center section and the not the other areas along the span.
Any how i don't know if it will be more effective than Mclaren's.