Shattering Impact takes effect on every melee hit from weapons with any Impact damage. It has no effect if the melee weapon's Impact damage is zero. Note that it is not necessary to proc the Impact status effect to trigger the armor reduction.
The amount of armor reduction per hit is a flat, constant value, independent of the amount of Impact damage inflicted. Since the reduction is applied to the target's base armor, for a given enemy type it will always take the same number of hits to completely drain the enemy's armor, regardless of its level.
Compared to Corrosive statuses, Shattering Impact has the ability to reduce a target's armor to 0 instead of just by 80%. Corrosive, however, only needs 10 procs to achieve this, while Shattering Impact may require a substantially higher amount of hits for the same effect on enemies with high base armor.
Shattering Impact is able to affect status immune enemies, such as bosses.
As of Hotfix 18.1.4 (2015-12-21) Shattering Impact doesn't reduce enemy armor when used with the charge attacks of thrown weapons. The charge attack from a Blade and Whip type weapon will however reduce enemy armor.
The mod is most useful against enemies with low amounts of base armor, and at high enemy levels.
The mod is most useful on melee weapons with high attack speed, and on stances which involve applying multiple discrete instances of damage on the same keystroke. Due to its demand for high attack speed, this mod has good synergy with Fury, Berserker Fury, Quickening and Gladiator Vice.
The Heavy Attacks of the Sarpa, Arum Spinosa, and Vastilok all fire multiple projectiles that have a portion of Impact damage, allowing players to strip armor from a safer distance.
This mod does not have a description in the Polish Warframe Client.
Very often the armor reduction from Shattering Impact appears to only be able to be applied by the host as the health bar remains yellow for the clients. However, the actual effects from the armor stripping are applicable for the whole squad.