The masks on the cowls make the cowl buggy for some races, Im Argonian, and while I probably expected the mask not to appear, the cowl didint appear at all, and it took away my hair (horns)
Although it did keep the stats there, as well as letting me put on another hat/helmet, however, it only keeps the magic bonuses, not the protection, say I were to put on the cowl then a hide helmet, it would keep the protection rating of the helm while keeping the magic bonus of the cowl.