We've just cracked and bought one for DDog3.
She's excitable, licky, springy and hugely reactive outside the house. We've just put it on her and she's rooted to the spot bizarrely calm. We can stroke her without being drowned in dribble, she's not jumping up, in fact she's almost catatonic. I can hardly wait to try her outdoors 
However hard I've looked, I can't seem to find any guidance on how we actually use it though. Should we keep it on all the time or use it only in situations where we know there's going to be an issue? ATM
I may never take it off as she's cheerfully pottering about the house and not causing mayhem in any shape or form. I'm worried that the effects will be diluted if we use it constantly, but perhaps prolonged periods of behaving "properly" may cause her to see that as normal (as we are hugely praising her at the moment for her calmness)
I really don't want to ruin this "miracle cure" by using it inappropriately.