This robe is good for any int class, probably with the chanter benefiting most (the added cha).
Yes, Cha does do something for charm. Its a secondary resist check, and the higher cha, the longer charm will last, not lasting longer than full duration of the used charm spell/song ofcourse.
The negative stats looks bad, but really isnt. 8 AGI is compared to 1 or 2 AC, and since int casters have crap AC, they will get hit for full damage anyway.
To sumarize: 80 raw mana is great, and if you havent maxed yout int, then you will get an extra 60 mana for the int at level 60.