[Myron Piatek]

As far as I know, there are no disadvantages!
It is much more durable than rubber, "gives" less but still absorbs vibration, lasts indefinitely under normal use and therefore will not cause the back of the engine/trans assembly to move around and/or settle like old, worn out rubber mounts will do. Worn out rubber mounts will cause header clearance and driveshaft alignment/pinion angle problems.