The Black Dragon Shield is a very powerful all-around shield with strong elemental defenses, allowing it to reliably block almost all forms of damage. Its decent stability makes it useful for warding off most forms of physical attacks.
However, it is also only available as a random drop in the very last area in the main game, meaning that its utility will be very limited. As well, like all other Black Dragon equipment, it requires the use of Petrified Dragon Bone to upgrade. Finally, it is one of the heavier medium shields in the game, meaning that equipping it may negatively impact players' mobility and equipment options.