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.
The Cerberus Harrier is highly recommended for long range shooting if you stay out of cover, as it decreases recoil greatly. It also helps at close range too, where its fast rate of fire can be used to land a great deal of headshots quickly to efficiently eliminate foes from the fight.
Contrary to the weapon 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 is much more beneficial to overall accuracy if you fire out of cover.
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.
Contrary to the weapon description, the Harrier actually deals slightly more damage per round than the Mattock.
The Barrel and Piercing mods or Armor-Piercing Ammo really benefit this rifle. Being unable to penetrate shields or plating is the second biggest flaw besides recoil, and these additions somewhat alleviate this problem.
Another shortcoming to the Harrier is ammo capacity. The Harrier fires at a relatively fast fire rate and will chew through ammo. This can be resolved by using the spare ammunition evolutions of the batarian class power, Batarian Enforcer. Another option is the Extended Clip Capacity mod, which brings the clip size up to 28-36 rounds before needing a reload. This allows both a longer and deadlier hail of gunfire on enemies.
The N7 Demolisher is best paired with this weapon due to the never ending ammo supply allowed by Supply Pylon. An N7 Destroyer taking advantage of another player's Supply Pylon may be even more effective.
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 the Geth Prime, or Atlases.
The Thermal Clip Storage Gear is very useful on this weapon, as it helps to fight the gun's main weakness; its low ammo count. With this upgrade, you will be provided with an additional 10%-30% ammo. The Barrage Upgrade gear is similarly useful, trading some of its ammo storage bonus for reduced recoil, mitigating another weakness of the Harrier.
With its fast rate of fire and low clip capacity, using the Harrier when fighting enemies at range, or enemies with ranged weapons, like the Collectors, can be difficult. Using the Supply Pylon or Devastator Mode can assist in negating this problem.