Definitely calms unhappy cats
Feliway isn't magic but it definitely works. When I bought two Cornish Rex cats, my older Ragdoll cross was thoroughly miserable. The cats wouldn't be in the same room and hissed and fought. The first time I used Feliway it didn't work as they were too angry but when I tried it a month later there was a noticable, permanent calming. I used it for six months and then stopped. Recently, my boy cat started fur plucking and attacking my other cats. Feliway worked almost instantly this time.