First off: I have ordered hundreds of products from Amazon and believe this is only the second time I’ve taken the time to leave a product review. In my opinion, this is an important category if you are a dog lover, so just want to help educate.I ordered the dog collar / remote, as well as two additional collars. All arrived within two days and were very easy to set up. I have not had to use customer service yet, but this might be one of the most proactive C/S departments I’ve encountered. I received e-mails, both before and after my packages arrived which included the owners manual and links to videos to aid in setup / programming. Again, programming was very straight forward and the collars keep their memory which is one of the reasons I went with this brand.I have a 12yr old Blue Heeler/ Beagle mix and a 4yr old German Shepherd. My GSD was a rescue who had a rough 1st couple of years (before finding us) and does show aggression out of fear towards other animals and some people, as he was not socialized as a pup. He is a work in progress and is a big baby with my family. We were recently contacted by the same place we got GSD#1 to see if we’d consider GSD#2, who is approximately 1 year old and also a male. We were hesitant because of the obvious, but was confident that this could end up helping GSD#1 as GSD#2 was a confident, social dog. I took a week off of work to introduce Stone into our pack. The 1st introduction took place on neutral ground at a friends pond. I had my son take GSD#1 (Rambo) to one side and I took Stone to the other. As predicted, Rambo went into all out war mode the second he spotted Stone, who was 60 yards away. He is very protective of my family as GSD’s often are. My wife was convinced this would never work. We did some passes at 10-15 yards away (both dogs on leash) but the tension never subsided. I then let Stone into our house and on our property without our other two dogs. Then removed him and brought them in to start getting used to his scent. The 1st few days, we could not let them in the same room together. Again, my wife was very skeptical. I strongly believe her anxiety also fueled much of the early fire. After working with them on leashes in our yard for a couple days, I then put them in muzzles and started bringing them closer. Rambo was letting hm closer but was a coiled spring of tension. I then introduced the collars. I started by buzzing (vibrate mode) anytime I saw any look of aggression from either of them. We have invisible fence, so this sensation immediately resonated with Rambo. I then let them roam the house together in muzzles and kept with the buzz vs. aggression routine. The 1st day, I did keep Stone on leash in our house just to ensure I had positive control. Then, the defining moment: They were having a tense day, so I waited until I was home alone with the dogs in order to keep the air calm. I let Rambo outside 1st and waited a few minutes. I then brought Stone outside on leash...both with collars on. I anticipated Rambo coming after Stone and decided that if it escalated to a fight, that he was going to receive his 1st shock. That’s exactly what happened. I made it 20 ft out the door and Rambo lunged at Stone which resulted in a dog fight. The second he attacked, I corrected him. That ended the fight immediately. To my astonishment, not only did this end the fight but it caused Rambo to submit. I suppose in his mind, Stone has electrical super powers and does not want to mess with him. I have had Stone for exactly one week today. If you consider where we started, where we are now is nothing short of amazing. 99% positive reinforcement along with help from these collars and my household is almost calm. I use the collars less each day and have only delivered a total of 3 shocks. 2 to Rambo and 1 to Stone. All other corrections are in vibrate mode. When looking at these pictures, envision 2 dogs that wanted to kill each other from across a pond one week ago and the Black and Tan (Rambo) who would never allow another dog in his house and the blonde (Stone) who only wants to play but will never back down. Our other dog really just try’s to keep his distance. He’s too old to mess with these two.The product literature recommends not using these collars for an aggressive dog. I’m here to say that these collars are helping me re-train him with another non aggressive dog and anticipate not needing these collars in the near future. A happy and safe dog is a dog that is trained and knows his boundaries... these collars were the answer for me. To my lovely wife - Told ya so!