A Rank 1 Seeker is sufficient to pass right through the metal shields of Shield Lancers. Increasing this mod's level will allow a massive crowd control, as it pierces dead bodies and enemies. This mod is also great for using your friends as a shield in close quarters combat, as you can shoot through them.
When equipped to any non-hitscan secondary weapon and used against General Sargas Ruk, you will deal very visibly multiplied damage versus his weakspots.