We used one when we first got Millie 3 & 1/2 months ago. What a difference it made in Chester. We really learned so much. We now have a happy dog family where they get along great. Wasn't always the case, though. Chester was very agressive towards ALL dogs, especially males. We also had a few issues with Millie and worked on those, too, but the biggest help was with Chester's aggression. I know it's not always this easy, but he's even so-so with some male dogs now. If you see the right person, and are comfortable with what they're telling you to do, then it's so worth the $. Ours was so helpful, and we still call him with questions every once in a while.