It really works!
I bought this when I introduced a new kitten to the household where I already have a 5 year old cat. My older cat was desperate to be close to the kitten and he showed zero signs of distress or aggression. How do I know it works? Well after 2 months I hadn't realised that the latest refill in had run out and wondered why my older cat was hissing at the kitten quite often, I put a new refill in and almost immediately he stopped hissing and they were playing again!