I think if we ever see an alien, he will either fly to us in a completely enormous nuclear rocket which we will spot years before his arrival and deceleration. This is in the case if there is really no other way to traverse stars besides conventional rocketry. But in case if there is a way to trick any of the fundamental physics we know after all, then very likely the guy will come right at our porch, and they've pro…
We have stealth techonology, don't we?
Inertia control is not needed if you can create a field. The problem with acceleration is that it needs to be transmited from the engine to the human body. That happens through the seat in planes or rockets.
But if you were able to create a field that uniformly affected all the molecules of everything into the ship, including human bodies, you could perform sudden turns without crushing the crew.