That seems to be the case. I don't know whether the duration is affected by how long you fire (like in the case of the B-Wing's rapid fire ion cannon, you could shoot that thing for a while).

The primary use anti-fighter wise is the fact it travels much faster than your lasers and can disable the guy while you go in for a kill, I suppose. Still, I usually just use ion cannons for anti-cap ship work as sometimes it helps if you've got quite a few guns on you.