Unmitigated bushwa. Most aircraft engines (fixed pitch & CS prop) will stop
the prop at normal glide speeds.

Never had an engine failure, have you?

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford





Also just shutting off the engine doesn't stop the prop from windmilling.
To do that you have to have a prop that fully feathers and even then they
don't always stop fully.