Every bit of external bling adds to drag for sure. The visor is mesh
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and fairly streamlined. I've never had one rattle, move or fall off. We have them on EVERY farm vehicle (5). To be honest, I never considered drag. It would be so small to be almost irrelevant.
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I've had a sun visor on all my cars except one.

I Luv em!! They reduce heat and give my hands some shade when driving.