About the "pain" or "discomfort" of a prong....
I had mentioned that a prong was a good tool when used properly. When used properly, there is no pain, nor discomfort, except for maybe a puller the first time the prong goes on.
What I mean when I say power steering is that they can feel the slight pressure. Correct use of a prong does not implement pop-corrections. A dog, their first time with one on, might go to the end of the leash once or twice, but after that, they know its there and usually don't (though some heavy pullers might ignore it).
The best thing I can compare it to is a bit in a horses mouth. Typically you start training with a snaffle - a light bit. Sometimes, as horse progresses in training, you need to go to a heavier bit or one of a different shape. One that the horse will feel the slightest change in your hands. This is what a prong is like. The dog can actually feel the collar cues, not in an uncomfortable way, but just be able to feel that there is a cue. Power steering. The slightest cue is felt.
Correct usage does not inflict pain. If you think about it, anything around the dog's neck keeping it from where it wants to go has to be uncomfortable. The key is that we are teaching the dog that it WANTS to be with us. I believe that dogs get used to the pressure on their necks and learn to ignore it. When I use a prong, it is usually to refine heeling, so that the dog can feel when it is out of position. It is never used to actually correct (in the "pop" correction kind of way). And if I am using it to stop a puller, I use two collars and two leashes the first few times so that the dog does not all of a sudden lunge to the end of the leash and get a hard correction with the prong. One collar is a flat collar, the other the prong. I hold the prong leash slightly looser than the flat collar leash. When the dog hits the end of the flat collar leash, I apply pressure with the prong. It doesn't take them long to figure out not to lunge out...
Every collar out there can be used in a cruel manner. At my dog club, we have a few Kohler-type trainers. A friend of mine has been using an e-collar on his Rottie (very high drive, silly boy) because he was having problems with everything else. The trainers at the club told him that they don't want to see the e-collar in the building anymore. They have no problem with stringing a dog up on a choke chain when it misbehaves, but refuse to allow proper stim usage of an e-collar. I was at a puppy class at a different club where the trainer said that the only collar you can actually give correction to a dog with is a choke collar. What???? Any pop on anything that is attached to something wrapped around your dog's neck IS a correction, no matter what it is that is around that dog's neck.
Any correction based training is about making the dog uncomfortable when it does not do the desired behavior. My stand on prong collars is that when used correctly, an actual correction is never needed....