I had always heard of them being called shock collars and just knew many didn't agree with their use. The trainer asked if we had ever felt an e-collar, which we hadn't. So he had us hold it and feel the various levels. Many of the lower levels couldn't even be felt. Once I could feel it, it didn't hurt, just tingled much like a TENS unit used in physical therapy.
This is an excellent video showing a family wife, husband, and child experiencing an e-collar for the first time.
The e-collar allows us to get our dog's attention as well as communicate with our dogs non-verbally and at a distance. It is used in combination with many other training methods.
There are rumors that say we keep remotes in our pockets or wear bandanas to hide the fact that we use an e-collar.
Remotes are in pockets (or clipped to a waistband) a lot after the dog has grasped the basics because they are not used very often.
The bandanas are actually recommended for dogs who are out with the public a lot to remind owners to do a hand check before communicating with their dog. We found when bandanas were not worn, people would pet the underside of the dog's neck and kids would play with with the collar. Since we sometimes communicate with our dogs through the e-collar we do not want to surprise someone with an unexpected tingle.