The mysterious Mechanist has unleashed a horde of evil robots into the Commonwealth, including the devious robobrain. Hunt them down and harvest their parts to build and mod your own custom robot companions. Choose from hundreds of mods; mixing limbs, armor, abilities, and weapons like the all-new lightning chain gun. Even customize their paint schemes and choose their voices!
Installing the add-on adds a couple of new idle comments to most companions' repertoire. These lines revolve around robots and let the Sole Survivor's followers express their opinion of the machines in various ways depending on personality. If an automatron built by the player character shares a settlement with an organic companion or is currently traveling with the Survivor, their updated comments tend to make up the majority of their idle chatter when they get within earshot.
Similar to above, a small number of new loading screens are added to the basic ones as soon as Mechanical Menace is started in earnest. They seem to replace the normal loading screens almost completely even after the Automatron questline has been finished, severely limiting the overall choice of loading screens one gets to see.