Worked for me - six cats all visiting my back garden, two of them every day, leaving little "presents" for me to dispose of. The range is about 4 or 5 metres I'd say, and I bought it because it holds a lot of water and doesn't need batteries.
1st cat visit: He looks at me strangely while I point and shoot. The water barely reaches him but he runs off immediately.
2nd cat visit: He runs off as soon as he sees the gun when I open the back door.
3rd cat visit: He runs off as soon as he see me open the back door.
4th cat visit: There isn't one. :)