My tractor has an operator presence switch, and it can be overridden by flipping the seat forward.
However, since I don't normally flip the seat forward when getting off the tractor, if I mistakenly get off the tractor with the PTO running, the tractor dies. Which is correct - I did something more unsafe than usual, and it potentially kept me from getting hurt at a minor inconvenience.
On the other hand, if the rare occasion arises where I need to get off the tractor with the PTO running, I can flip the set forward. But, this forces me to think, "I need to flip the seat forward because I am about to do something potentially more dangerous than normal." Since I'm specifically thinking about this, I am safer than if I were doing the same ol' routine.
This is true of many safety interlocks. They are a pain occasionally, but if they ever force you to think twice about what you're about to do, maybe they are worth it.
So, I think the system works fairly well.