The vibration is not a shock and is not very strong. In fact, many people who have used the collars worried at first that they wouldn't work because the dog didn't even seem to notice. But with conditioning and training, your dog will respond to the vibration. The vibration signal for a deaf dog becomes the equivalent of using voice to get the attention of your hearing dog. Many people just assume that since their dog can hear them, it will obey them when off-leash, which is not the case.
Every dog is trained and obeys at a different level.
This is true of a deaf dog using a vibrating collar also. Every dog must be treated and seen as an individual and you must take that into account. Before You Start A vibrating collar is not the answer to your training problems. It is not a magical device that will make your stubborn or rambunctious pup pay attention to you. It is a tool that will allow you to better communicate with your deaf pup.