Couple of points,
First, It's there to protect the case of pilot incapacitation, better than flying off as a zombie.
Second, it is easily overridden by the pilot. Disconnect the A/P and it's done.
Third, it does NOT deploy speedbrakes, so the descent will not be really rapid giving more time for pilot intervention. I'd guess none of the planes so equipped would descend from F450 Ag much greater than 1500 fpm clean.
Last, to the best of my knowledge, it's hasn't yet been used for real.
GF