For some cats it seems to work, for others not.
I only really know about the plugin as it has sparked my attention since it came out, and I know about 1-3 months can pass with it's usage before you will see any real effects.
Hollie. I have a large couch-hide a bed, and my cats were constantly scratching it up, even after I made for them a scratching post. So, I had to cover the furniture with blankets and bed spreads. Now, once in a while I'll catch one or two of them scratching on it, but a quick squirt of water tells them I do not like that behavior.