We used to call those things "choppers".
There's some merit in fan blades flattening out with RPM, and I seem to recall a GM version in the '70s or so.
Plus they're not made from Chinesium, or riveted together by people who are free of liability.
My point is, if you can't run a dis-engaging coupling, at least lose the blade pitch with RPM.
Of course, an electric puller fan can also work with no HP loss.