Both cards
Scary idea, I'd admit. One thing, though: what they will show when there are less than three cards in the target deck?
Insight-specific
If the AI plays it, true, it pretty much does nothing. In a match between two skilled players, though, it's another story.
Its value, methinks, is about as good as the enemy's deck; a shoddily-built opposing deck will give you no significant insights on what they're actually up to, pun intended.