Hi,
actually I don´t think that any standard grill will reduce the air flow very much. This is relative to the air that will "flow" through the radiator. The amount of air going through the radiator must really pushed/forced through. Take a look how tight the holes in the radiator are- compared to the grill!
When you are driving you will push a lot of air in front of you and around the front-but due to the radiator itself not the grill.