These Cerberus-modified Mattock rifles are fully automatic. Cerberus gunsmiths reined in the recoil issues, resulting in a gun that stays on target but delivers slightly less punch per round than a standard Mattock. As such, the weapon is typically utilized by Cerberus’s elite troopers who train constantly to make every burst count.
Despite the weapon's description, the Harrier has much higher recoil than the Mattock - using a Stabilization Module (both on the gun itself and as an armour upgrade) and a Scope can largely eliminate this problem. Marksman and the recoil reduction gained from the turian class power, Turian Veteran, can be highly beneficial, as it maximises RoF whilst reducing recoil.
Oddly, the Harrier seems to benefit from reduced recoil in situations where it would be expected to be harder to control; "from the hip" fire under cover and aiming while moving seem to keep it on-target better than aiming from cover. This is due to a bug in which the recoil values of the Harrier (in cover and out of cover) are inverted, meaning that it's a bit more beneficial to overall accuracy if you fire it out of cover. Again, classes with Marksman or bonuses to weapon stability, and/or Stabilization Modules makes this difference irrelevant.
The Harrier benefits greatly from the damage bonus and fresh magazine given by Adrenaline Rush.
The Harrier is easily one of the most powerful assault rifles throughout the game, as it deals excellent damage, is quite accurate, has a respectable clip load, and drawbacks that are easily mitigated. The only area it truly fares poorly is when engaging shielded targets, but even this can be mitigated with the proper ammunition, or having an alternate weapon for this purpose.
The Harrier deals the same damage per round than the Mattock.
The biggest flaw with the Harrier is ammo capacity. This can be resolved by doing the following:
The N7 Destroyer can use this weapon very effectively, since it gains more accuracy, a higher magazine size, rate of fire, and damage if Devastator Mode is active. The high damage of each shot from the Harrier can quickly deal with most smaller threats in very quick fashion, and can inflict noticeable damage on boss-units such as Geth Primes and Atlases.
With its fast rate of fire and low clip capacity, using the Harrier when fighting enemies at range, or enemies with ranged weapons, can be difficult. Using the Supply Pylon or Devastator Mode can assist in negating this problem.