Excellent Responses & Many Thanks

Thanks to all for your responses to my question.
The improvements they provided are understandable. I can see that the propeller blades would produce more thrust & give more cooling at the hub with them than without.
But than again if the manufactures knew this why did some a/c have them and others not. Such as the Grummen Wildcat versus the Grummen Hellcat. Or why didn’t such types as the P-39 & P-40 use them. These two needed any improvement in performance that one could find! Perhaps their mission altitude didn’t require them. Such as the P-51 warbirds now, who needs altitude performance when the mission is at lower altitudes.
During the war perhaps the production of aircraft numbers was more important than the advantage that the cuffs gave.
Thanks also for the update on the company which provides them now for installation on Mustangs. Looking forward to seeing them on Mustangs wherever possible. I like the looks!!