As a seeker, you'll often have access to the clues needed to get the bonus damage. We'll have to see how future Chapter 2 campaigns shake out, but in just the core, there are a startling number of enemies that have 3+ health even in the very first scenario, so there will be a lot of situations where this does not serve the job of "get the enemy off of me, permanently." Could still be worth playing, particularly if you have concerns about the rest of your party's ability to fight through an Elite enemy - being able to have your add in 2 damage will make it a lot easier for your fighters to defeat an enemy with 5 HP.