...Larry is Right! The Benefits have, or have not, actually been proven.
All I know is Hot Air comes out of them, and If You have 'A Windshield Cowling Intake 'Vent', as I cut in a 'Secret, Hidden Location' (and closable) for Ventilation...You'll feel some of the heat enter the Cabin.
The 'Hood Vents' were already On my car when I purchased it. They were the Original? Older, Large, with a Wide Border. They Looked Ugly, as a 'Hibotchy Grill'! I took those off, sold them and Replaced them with the Newer Design, You Now can see. Showing just a Row of Fins. Gorgeous!! NO More cutting was necessary...they fit right in, Correctly! I painted the 'Fins' Satin Black, and the Hood Flat Black. I Left the Screens OUT, they don't Look Good, in My Opinion.
As a Fact...I just finished replacing the Vent Mounting Studs with Stainless 'Button-Head' Allen Machine Screws. The Threads are 6-32. I installed them with a Tiny Stainless Washer (Load Spreader). NO Longer, are there un-sightly, Rusty Nuts, showing!
As Larry implied...THINK Long and Hard, before Cutting the Hood!!
...There's NO Going Back!!
MJ