Q: Will the deflectors add downforce or mainly change the look?

Their main job is reducing turbulent air pressure and drag around the front wheels, working together with the front lip spoiler, rather than generating big downforce numbers on their own. The visual change is significant, a wider, more aggressive stance. If outright front-end downforce is the goal, adding the canards and racing diffuser from the front aero kit is where the real aerodynamic load comes from. The deflectors set that up.