need more info about sub magic devices!

i want to make a magic warrior class but i'm still confused about the sub weapon stat cuz i never use it.
which stats from magic devices will be used if i set it to sub weapon?
for example :
Fireworks
[magic devices] ATK: 252 (35%)

Fire element
MaxMP +1000
Additional Magic 100%
Recoil +0.01%

Base ATK: (250)
Refine: (5)
sorry if i have a bad english.

 

You only need the element, other stats dont matter. The refine count does increase your matk, though

 

thank you for the info !

 

Ah I got it slightly wrong, refine count doesn't directly increase your matk, but the resonance buff of magic swordsman skilltree will be enhanced based on the MD's refinement. Resonance gives random buff though so you won't always get matk buff

 

by default, only the appearance matters.
stats, crysta and refinement are ignored.
also, your atk decreases by -15%.

Magic Warrior Mastery lessens the atk penalty to -5%.
Ether Flare and Element Slash apply the MD's element instead of your main weapon's element.
Resonance boosts it's buff effects based on the refinement level of the MD.

so appearance, element and refinement matter, but stats are ignored.
if you refine at the NPC, it is better to use a low atk MD, since the spina cost scales with weapon atk. refining Fireworks will be super expensive and give no benefit over Elflame.