In the US both aircraft takoffs would be not approved; illegal. Even under Part 91. Let alone what the insurance company would say about it if anything would have happened.
First takeoff, the slope of the runway exceeded 3%. The runway was too short for a balanced field operation.
The same for the last video in the Mustang's takoff in the US.
Under Part 91 (private aircraft regulations), jet aircraft operations must comply with the certification limits and requirments set forth in the Aircraft Performance/Operations Manual, including the takoff profile; balanced field length, second segment limitations, etc.
Exceed or not comply with those and you are in voilation of FARs.
Just like taking off over weight in a Cessna 172, it is illegal.