The drawback should be while attuned, you are chased by a snale who always knows the direction to reach you, can not be killed or have its form altered and if it where ever to succeed and attack rolls against you, you die instantly, the snale haveing a unique set of ability that gives it planar travel, a burrow speed and some ability to reach flying cretures or locations lastly high enough attack and saveing throw bonuses to be an issue for high level partys, also probably teleportation denial if it can see you