I am testing it right now and it doesnt seem to do anything to your weapon except give a +1 enhancement bonus. the description said it would turn your weapon(s) to shadow blade(s) and change the material type to force.
shadow blades get charisma modifier to attack and damage. I am a little confused with the enchant and what it is supposed to do with the weapon I am using. the weapon is doing slashing damage and got adamantium as material type, the charisma to hit and damage isnt there. the familiars charisma to hit and damage works though.
Is this a bug or wasnt the information updated? oh well.. I just thought it would be cool to imbue the sword of shadows with shadows.