dog training collar 800M remote rechargeable and waterproof dog trainer for 3 dogs

At first I was a little iffy about buying this because I was worried that it would hurt my dog but so far so good. One of my dogs（8 years old） always bark and nip at people when they get close to her. I tested it on myself first so I wouldn't hurt my dog. I have only used the beep and the vibration modes on him and he does respond to it very well. I did use the shock at below 30 on my another dog and it really got her spooked. Both of my two dogs weigh more than 60 pounds, so they are not puppies. Thank you so much for a non expensive way to help train my dogs without hurting them.