I have two mini aussies (siblings) who are fully trained and are perfectly obedient in every way, except for one thing... I live behind a school and there is a path that runs along my house and a track behind where people run. Prime barking territory for my dogs as people and dogs are always passing by either the path or going around the track
I bought two of these collars, one for each dog, hoping that the remotes would work independantly. They don't. One remote will trigger both collars, so I sent one back. It was just as well though, because my male dog, Clyde, only needed to be sprayed once and he was done. Now just his sister, Bonnie, barking is enough to back him away from the fence. He's the more timid of the two and this collar isn't a good idea for him. He freaked out after the first spray and sometimes still gets scared just from Bonnie getting sprayed.
Bonnie, however, has a bolder personality and can handle the spray. She's still a little more persistent in her desire to bark, but she doesn't bark near as much as she used to. But once in a while she'll see a dog she doesn't like and go off, that's when the spray is needed and it works to get her back under control.
All in all, this was a great buy. Just be sure your dog's personality is strong enough to handle it.