How is it possible to hit with this thing ?
its always missing

You need to keep the lock after launch, it's good in that if you lose the lock on the target you can reengage. If you can get after a flares pop you can get a hit - just be wary if they go behind a hill or get below radar it can miss then. I started on it yesterday, it's a bit of a learning curve but so far I've had a better hit rate.