It is a unique shock baton. Unlike the regular shock baton, this weapon doesn't do shock damage. However, when it scores a critical strike, the target will fall to the ground just like the knockdown effect of the Victory rifle or the scoped Gauss rifle. Unlike the Paralyzing Palm perk, it doesn't depend on the use of V.A.T.S. for its knockdown effect - instead, it is triggered by every critical strike (though the stun only lasts for two seconds). Since it only requires 15 AP though, it is a good weapon to use with V.A.T.S.
Although it has a high base damage it does not do as much overall damage as the shock baton due to the lack of shock damage, but the knockdown effect does give an opportunity to deal a few more blows.
Enter the engine room during the generator-destruction phase of the main quest. Walk down the stairs and you will see a groove in the wall with a window. If you look through it you can actually see the weapon. Follow that corridor until you get into the big open area. Take a sharp left when you get to the open area, and then it will be your first left on the same wall you came in from. Go in that room and then follow the small corridor and at the end it will be lying on a table.
PCPlayStation 3Xbox 360 This weapon does not receive a bonus from the Xenotech Expert perk. This may have been intentional because of its unique effects.