The Tainted Shell mod reduces the spread of Shotgun fire by -7% per rank while also decreasing the fire rate by -5% per rank for a maximum of reduced spread by -77% and reduced fire rate by -55% at rank 10.
The DPS-averse nature of this mod, the opportunity cost of slotting it, and a high capacity requirement, give it a fairly narrow applicability..
The fire rate reduction can be counteracted by using Shotgun Spazz or similar, but if this was the primary reason to slot such a mod, it would cause the opportunity cost to effectively double.
Tigris, because of it's duplex trigger, can benefit from this mod with practically no drawback. Sancti Tigris comes with an innate polarity.
The decrease in fire rate increases the delay before the Tigris automatically reloads after emptying it's magazine. This can be remedied by pressing the Reload button right after firing the second shot
If Tigris is given more than 2 shots per magazine with appropriate mods, or if the weapon gets corrupted in a Void Fissure, the delay after every 2 shots is increased noticeably.
Similarly to the above, Exergis benefits from this mod, as it also has an innate polarity, and is able to ignore the fire rate penalty due to being single-shot.
This is true despite the weapon already having the second-narrowest firing cone of all shotguns, behind Astilla, since it also has an extremely low pellet count: this mod makes it easier to hit a target with all pellets, and deal full damage to it.
It is somewhat suitable for shotguns with a higher fire rate and wide spread like Boar and Boar Prime, as it makes it possible to concentrate fire on a single target, at distances greater than point-blank range.
Due to its lack of falloff damage, this mod is useful in decreasing the spread of Drakgoon allowing it to hit distant enemies more effectively, without charging the shot.
Adding this mod to Phage will narrow the initial cone of the beams.