That's ok, some people just know more than the manufacturer.
There are many factors to consider in any given situation of course however the chances of rotating blades under idle power breaking up and throwing some shrapnel and the damage likely to be caused by that is far less than the catastrophic damage to the airframe that will occur if a feathered prop possibly digs into the ground if on a dirt strip (and it can even happen on a paved runway).
In that case the entire engine being ripped off its mounts and the airframe and possibly taking the wing with it and opening up the fuel tanks are far far worse.
What a load of rubbish! That takes this week's pprune bullsh!t award.