Pros: Cat seems more calm
Cons: The powder that it releases (but it was ok after a while)
Well i bought this after reading about this in the forum here, because i recently moved with my cat from my home country to europe. My home country being Brazil, my cat has short hair and is adapted to going outside, having sun, etc. And in here there is no such thing and is a small apartment. My cat went nuts, needless to say. It would cry all night long and we couldn't sleep at all. I had to order the colar from amazon so it took like 2 weeks and a half to get here, and in the meantime the cat stopped crying all night. When it got here i put it on him immediately, and i really didn't notice much of a difference. It DOES look a little calmer (being that is such an active cat) but we still can't sleep during the night, because now the problem is that 3am is the playtime, so he tries to wake us up. But that has nothing to do with the collar effectiveness.
For me, i won't remove the collar for this month, because my cat needs to adapt and i think it is kind of helping him to do so. It's a big change, and if you have a kitty that is in a bizarre new place, that is really hard on them, so even if they will act out or not, it's better to prevent and get them something like this collar or the diffuser, to help them adapt, and so they can feel at home right away! :)
Hope it helped