You will get this message for only two of the F4U's: the F4U-C and the F4U-4. Both are perked, meaning they cost* you fighter perk points just like the Me 262 or the Tempest.
You can see your current perk balance on the clipboard in hangar.
How to get perks? In a nutshell: Kill a lot of other players
You get more perks for each kill when flying a high ENY value fighter (see the ENY values in the hangar plane list). Killing an enemy in a P-51B (ENY20) will get you four times the perks than doing the same ina P-51D (ENY5)
*=you get the perk cost refunded if you succesfully land your perk plane/vehicle