When I looked at the picture last night it seemed to be a very tight weave and it looks blocked on the bottom like the stock grill so it appeared that it would flow less.
Now looking at the picture it seems it is open all over but the area that directly opens towards the radiator is certainly more restrictive and the area where the stock one is blocked opens up right into the bumper beam which may cause considerable turbulence and effect how much air can go through the A/C element and then through the already small radiator. I am not an aerodynamics engineer so I can only speculate at this point and consider all the cars I have built and things like a billet grill causing cooling issues, etc. If I was to consider this grill I would want to know before I spent that kind of money on it.
Weight wise, adding weight to the nose of a FWD car is always a bad thing unless it is a drag car, that is just physics and adding weight anywhere to a car is not good, it is always best to take weight out unless it considerably unbalances the car or makes it unsafe. I have added weight to the front of my car in a big IC, oil cooler and splitter/undertray as well as catch can and LSD but I have also taken over 50 lbs out before I started and then notched the bumper beam to fully expose the A/C, radiator, oil cooler, etc....
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The lower grill certainly blocks air flow to the undersized stock IC as well as adds more weight, a net loss in performance in two areas.
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I like the way they look, I am just very careful to do real performance mods, especially on a real performance car.