I have 3 cats. They all have really different personalities. We got Calm Down to try on 2 of them.
This is Jilly-Boo.
We got her and Tiberius (story of how we got them
here) for Christmas. She is very calm and good with people. When we have guests over, she stays around to check them out. So we didn't need Calm Down for her at all.
And here's Tiberius.
He is scared of any loud noises. He is really sweet one on one with our family, but even moving your hand too fast will spook him. When we try to bring him around other people, he starts shaking, so we don't do that anymore. We thought Calm Down would benefit him the most.
And last, but not least, Charlie.
My dad actually found him stuck in a tree as a kitten. He shook the tree, and then caught him when he fell out. Even though my parents didn't want to have another cat, my sisters and I convinced them to let him stay. He is also really scared of loud noises and people. He is not as much terrified, like Tiberius is, but he just doesn't enjoy being around people much. But he is also really sweet once you get him alone. He ended up being the only one to benefit from the Calm Down.
We didn't notice any change with Jilly-Boo, since she's already a really chill cat. The only difference was that it seemed she was sleeping more.
Tiberius got more bold. He would come out to see us more often, but then he would get rough and start biting our hands playfully.
Charlie did really well after having the Calm Down. He became much more loving and would sit with us in bed. He reacted the way we hoped all of our cats would after having it.
Even though Charlie really did calm down, we hated how Tiberius was acting, so we stopped giving it to them.
We did use it again when we moved, so that the car ride would be less stressful for them. It seemed like they didn't meow as much, but who knows how they actually felt.
In the end, I would recommend that you at least try it on your cat to see what happens. The only reason we don't use it any more is because the Calm Downed Tiberius was a bit mean. But it did well on the other 2, so I would say those chances are pretty good.