Medium-range, semi-automatic rifle. The Mattock is a hybrid weapon with an assault rifle's low heat production and a sniper rifle's punch. Marksmen favor its increased power over that of an assault rifle to bring down hardened targets. Its lack of a full-auto setting is advertised as a feature rather than a shortcoming as it curbs a soldier's tendency to spray inaccurate fire under stress.
One issue with the Mattock is its relatively high weight. Despite it being lower than the M-76 Revenant, it is still quite heavy. This can make it difficult for those who need to use powers frequently to be combat effective. Despite this, it is lighter than an M-13 Raptor sniper rifle, at the cost of accuracy and rate of fire. The Raptor also has a scope equipped by default, freeing up space for another mod. Players may wish to take these factors into consideration when choosing either rifle, based on their playing style.
Higher weapon ranks, combined with certain power evolutions on Krogan Soldiers, Krogan Sentinels and Drell Vanguards, can still give you +200% power recharge, which makes it a great "lightweight" choice for those classes.
The Mattock can use a High Velocity Barrel and/or a piercing-capable ammo type to drastically increase its effectiveness against certain enemies like Cerberus Guardians, or armor-plated Husks/Cannibals. The Assault Rifle Magazine Upgrade mod is also pretty useful, given the Mattock's high damage but moderate capacity. It can make the Mattock into a very effective battle rifle with a good balance between ammo, damage, range, weight, and accuracy.
The Mattock (levels VI+) works very well when paired with a Turian Sentinel who, with the correct power evolutions, can still have a +200% power recharge. This is especially useful against geth, as it allows the player to repeatedly spam Overload (even while wearing Tech Armor) to drain the shields of enemies, and then use the scoped Mattock to headshot them repeatedly. It's also a solid choice for the Turian Ghost Infiltrator, who benefits from enourmous bonuses to weapon damage and stability, and has an extra 20% assault rifle damage bonus at the end of his Tactical Cloak tree.
While the Mattock is primarily a medium range weapon, it can be used effectively at close range if it has an extended magazine and if the player has a fast trigger finger.
Adrenaline Rush turns this already powerful weapon into a deadly combat rifle capable of dealing serious damage to even the biggest of enemies. In the 6.8 seconds given, you can easily squeeze off at least 30 rounds, even more if you are good at reload-cancelling and trigger pulling. This allows one to dispose of whole groups of infantry with surprising speed, especially with Piercing and Barrel Mods combined.