My little cross uses one and it is great.
He started shadow chasing and a few other obsessive behaviours. He was first given Skullcap and Valerian which caused him distress. On it he became confused and aggressive. He had even bitten one of his favourite human friends.
We then tried the dap collar and he has been so calm and laid back. So much so I can tell when the collar needs replacing as he starts his shadow chasing again.
Of course each dog is different and what works for mine may not work for yours. But in our case it is fantabulous