It simply doesn't work. The developer will try to tell you that it's because you're doing something wrong. You're not. Maybe it needs constant updates, but whatever the case may be, it simply doesn't block ads consistently. Maybe find out another way to implement updates through the addon itself. I was thinking of buying it too, seems like a good one time deal. But now I don't know, because if that keeps happening in the future it's not gonna be optimal.

Edit: I've seen the developer response, the addon seems to work fine. I'm still not sure though, I'll have to use it more. Because even when it was working before, sometimes ads would still appear and I'd have to re-install. Maybe if it updates internally now it will stay functional.

Edit 2: I thought there was a security risk because I received an email from the developer, but it turns out that only chrome had that problem. The addon is really really great!!