I used the prong collar for Buddy on walks because he could
literally pull me off my feet using just the flat or training (chain)
collar. Even though he was trained the old fashioned Koehler
method, I could not give a correction(or didn't want to) hard
enough for him to listen & stop pulling. The prong collar went
on when we walked outside & came off the minute we came
back in. It's sometimes called "power steering" for dogs. He
never gave any indication of pain or discomfort wearing it.
In fact it was my vet who recommended it to me. BUT Wolf_Q,
for what you say you want to use it for, I really think Candy's
idea about training for the "lunging" problem is a better idea.
I think the prong collar used in the right way & for certain dogs
is not bad in itself. Some dogs don't lunge playfully, but they
are terrible "pullers" when walking. So I think for some dogs
in some situations, it can be a good alternative.