Spoiler I don't think there's anything to suggest Vader has forgotten about the Carrion Spike. And he doesn't strike me as the sort of warrior to want to rely on stealth technology, except in extreme cases like this. Vader can't deflect slugs back at the shooters. That they were throwaway was the point; he was using them as disposable in order to slowly build up his own knowledge of Vader. Same as any prequel story, then. But the tension comes from trying to work out why they're hunting each other, and how it will be resolved. Tarkin walking out into no man's land had a great air of finality about it even though we know the outcome. It's one of those examples of something being compelling enough to make you briefly forget you know how the story goes as you're reading.