Yeah, I always feel really comfortable around a dog that has one of those things on it's neck. If that's what it takes to control an animal, the owners can tell me till their blue in the face what a wonderful pet they have and how it wouldn't hurt a flea, and ya know what? I won't believe them!
You know why I'd believe them? Because I respect that they are people who believe in training their dog, not being yanked around by a rambunctious dog while they plead for the dog to heel. It's called a pinch collar. They work well on large dogs because you don't have to be rough with them and you don't need brute strength to have nice responsive reactions to leash corrections. I would much rather see people using a pinch collar softly than a dog that lunges at the end of a leash with a leather collar, or a dog that will choke himself with a regular choker.
Pinch collars are used by many many people in training their dogs... I use them and swear by them for training big dogs without a lot of brute force. They aren't 'spikes' really, and they don't so much hurt as they do mimic the feeling on the neck they'd feel when their mother, or a dominant dog, plotzes them by holding them by the back of the neck. They don't work because they hurt (they don't) they work because they speak to a part of the dog's psyche that they instinctively understand.
Please do something for me... next time you are at a pet store go to one of these collars, put it around your leg and yank on it. I'm serious. They do ~NOT~ hurt like you think they do. They are psychological to the dog, not cruel.
Good explanation on pinch collars.