Hey there Sunny,
I see there are a lot of things your not so sure about. Why don't you take it easy there big guy. For one the bottom grilles are no your main sorce of air intake. That great big grille above takes in most of the air. Besides they would not have put the skid plate under the car if they really wanted the main source of air flow coming in from the bottom.
What you think the mesh is, its not. The holes in the mesh are not as small as you think. And if makes you more comfortable. The other version of the grilles mesh holes are almost the same size as the originals.
Its funny though. I never said they were make your car spectacular, but I did notice that even in 100+ heat, the car is still running cooler then it was before.