The robe could be worn by races other than just mind flayers, but since mind flayers created them, it would have made illithids curious about why a non-illithid possessed one.
When a robe was put on, the wearer would notice that the robe would adjust to their height, width, and even their stride. Because of this, it improved one's ability to dodge attacks. Beyond this, the robe also conferred body equilibrium, body weaponry, and cell adjustment once each per day by utilizing psionic energy. The last was only usable on the wearer.
When body equilibrium was utilized, it lengthened and stiffened, and allowed the user to go over normally impassable objects. It also assisted in slowing a user's fall since the robes would swell up much like a balloon and cause the user to float harmlessly to the ground.
When body weaponry was utilized, the sleeves would shoot out and wind together into the wearer's choice of weapons.
When cell adjustment was utilized, the robe would squeeze tight to the user's body, and pulse with psionic energy as it healed wounds and cured diseases from the wearer.