Spectral Shields are best used on ships that engage in close combat. Most weapons that are used at this range are Energy-based, allowing your shields to last much longer.
They also offer the most shield energy for Xeno Division Hulls and below, making them useful against Alien Damage, which cannot be resisted by any of the basic shields. They are also often used simply because it is difficult to predict what damage types your ships will go up against, and this shield gives the most overall protectiom.
While Spectral Shields have high capacity, they take up a huge chunk of your ship's mass, with the same mass efficiency as that of Shockwave Shields and Deflector Shields.
Hulls that have active Spectral Shields glow yellow.