Shelteez reminded me that they are more often being called a slip collar or slip chain now. Our dog class trainer was very careful to show how to put it on, and how to use it so that it didn't choke the dog, but worked the way Shelteez described. I've also heard it referred to as a training collar, and that the "snap" is not so much a correction as it is to focus the dog's attention back to what they are doing.

Our instructor encouraged it especially so that the dog has a specific collar associated with a training session. She spoke about a lot of varying reinforcements such as treats, the clicker trainers, and good old fashioned praise. I felt she explained things pretty well.

For a dog that is bad with pulling, I personally really prefer the halti collar.