The EN is for Xeno Division Hulls only, and compared to the ENAL Heavy Talonite Armor in terms of effectiveness, the ENAL is better because it offers alien resistance in addition to its energy resistance. Comparing which ones to equip on the Punisher Cruiser, the ENAL is a better choice because it can offer a greater deal of protection while not taking up too much mass due to the mass reductions In armor. They are also are usually not used as the EXAL Heavy Talonite Armor is better in PvP/PvB and the PRAL Heavy Talonite Armor is better in base attacks.
They are also limited in number. Unlike blueprints, players cannot equip them limitless on their ships, the number they can equip depends on the amount of EN Heavy Talonite Armor items they have.They are also incredibly hard to get as a mid level player as the player has to hit Alien Fleets that are rather hard on higher levels and still do massive damage on lower level fleets with the wrong setup or strategy. Unlike credits, they can be re-used but require a refit time.