[Rooks]

Whats the difference between the two?

[Jack_Spade]

Frills are for attack, the weave is for defense.

[Hibiki54]

Shockweave is used during Clinch and Grappling attacks. You can be the attacker or defender, doesn't matter.

[Novocrane]

You can be the attacker or defender, doesn't matter.

This armor modification cannot be used offensively

[Rooks]

Except the description of Shock frills is :"inflicting Electricity damage to anyone that touches you" and  "Shock weave delivers a moderate shock to anyone making contact with the protected area... This armor modification cannot be used offensively." I figure you could at least use both if you are body slamming a person or shockweave if you are giving a person a bear hug.

[Herr Brackhaus]

Shock Weave can also be used with the Block action.

[ScytheKnight]

Plus Shock Weave isn't an obvious modification while Shock Frills are fairly obvious.