This is the most underrated BLU piece in the game, mostly because people don't understand how BLU physical spells work. If you have Blue Magic Skill merits, in a lot of cases this piece will bump you up a tier and being in a higher tier will do more damage than any STR and DEX headpiece, including Maat's Cap.
We all know Dynamis can be a total snore-fest sometimes, but this is one piece that makes it worthwhile. Pushes you to 312 blue magic skill with full merits and AF1 body equipped.
Blue magic skill is the only known stat that increases the hidden "blue magic attack" parameter, other than Physical Spells Potency merits (only exception being Cannonball, which is boosted by defense as well).
If you can break a tier with this piece, then it can beat Maat's Cap and Gnadbhod's against high-level, high-defense mobs (assuming all hits connect). However, you shouldn't be using physical spells not named Cannonball on them in the first place...
Comparable to Saurian Helm for casting breaths. The HP bonus is lower, meaning lower damage cap, but the +5 magic skill helps with accuracy meaning you land unresisted more often.
Zabimaru is incorrect. Raising your Blue Magic skill a tier does provide a significant boost to physical spell damage, but not so much that spell mods cannot outdamage it. Maat's Cap and Gnadbhod's Helm will outdamage this on the big 3 and Vertical Cleave. Gnadbhod's is better for Cannonball too. Voyager Sallet can be equal or better than this for Big 3, but it can also be slightly worse.
The Skill+5 is excellent for landing debuffs, and the Breath bonus is obviously nice.