We rescued a spaniel 12 years ago. She was precious at the SPCA and for the first week. Smartie pants. She turned into the most aggressive, non-compliant brat who fear bit. We decided if we took her back she would probably be euthanized. She chased and bit our cats, our sweet one year old spaniel and would bite us if we touched her the wrong way. It was evident she was terribly abused. She flinched if you raised your hand and was incredibly frightened of sticks. Someone did a number on her head (and body )
We took her to a reputable dog trainer. He took her on the lead and within moments said, "This dog is trainable." He was right. We agreed to let him do what he needed to. He used the shock collar once on her. It was so sad to see. She was running away and would not come back. He zapped her and had us call her. She stopped, yelped and ran to us for "protection". That day changed her life and ours.
She has been a challenge at times, but today she is still with us. She is obedient and has yet to show any aggression towards our chickens. I would NEVER leave her unattended.
I realize that every animal and situation is unique. We have ultimately felt that single moment with the shock collar saved Lily's life. Even though she had "PTSD", it was worth it for us to be able to have some control over her.
As ravens said, of course it is an highly individual choice. For me, a few moments of deterent, how ever unpleasant for the pooch and used responsibly, far outweighs potential damage of going after your flock.