Quarians have spent centuries at perpetual salvage and ship repair--the survival of their species depends on this technical expertise.
Quarian engineers are elite support specialists with a talent for setting up ambushes and providing cover fire through the use of turrets. Their technical wizardry makes them crucial contributors on the battlefield.
Quarian Male Engineers are more directly suited for dealing with shields than their female counterparts due to their Arc Grenades.
Grenades do not operate on a cooldown, so anywhere from 1-9 Arc Grenades can be thrown at once. Due to this and the power's general versatility, Arc Grenades may eliminate the need to use Incinerate in favor of a heavy weapon, though this the possibility of devastating combos. Still, with good headshots, one can equip a powerful but heavy weapon such as a Revenant, (Black) Widow, or Claymore and be very effective.
Alternatively, taking Incinerate with a light loadout will enable the Quarian Male Engineer to deal significant extra damage through Tech Bursts and Fire Explosions.
Because Arc Grenade already deals double damage to shields and barriers, the Armor Damage evolution may be a better rank 6 choice, as it makes the grenade a similarly viable option for dealing with Banshees, Geth Primes, Pyros, and Brutes.
The Quarian Male Engineer can reliably set up Fire Explosions and Tech Bursts on its own when using area evolutions of Incinerate and Arc Grenade. Using Incinerate, then throwing an Arc Grenade detonates any Fire Explosions, and leaves whatever enemies that are left susceptible to a second Incinerate for a Tech Burst.
The Quarian Male Engineer can be a very potent support character when using the Movement Speed and the Area Scan evolutions. Area Scan will reveal all enemies within a very large radius of the enemy scanned, which can reveal cloaked enemies like Phantoms and Hunters. It can also be used "blind", where one does not target an enemy (though only with the Area Scan evolution). This can be useful if a smokescreen is set up.
Equipping a Falcon with Disruptor Ammo is a reliable way to prime and detonate Tech Bursts when throwing Arc Grenades, especially if the Electrical Damage evolution is taken. The area-of-effect damage that the Falcon deals will help set up and trigger Tech Bursts across multiple enemies.
In fact, with a Cryo-Ammo Falcon or equivalent explosive weapon, the Quarian Male Engineer is capable of setting up and detonating powerful Tech, Fire and Cryo Explosions in succession with Electrical Damage Arc Grenades and a high rank Incinerate. Shooting an enemy primes a Cryo Explosion detonated by Arc Grenades, which set up a Tech Burst detonated by Incinerate, which sets up a Fire Explosion detonated by Arc Grenades, which sets up a Tech Burst... ad infinitum. With Area Evolutions and Grenade Capacity, the Engineer can reduce huge groups of enemies and bosses to frozen electrified flaming rubble in seconds.
Grenades will very quickly tear through initial enemies or drastically weaken Atlas Mechs. Tactical scans can weaken Atlases even further and make them even more vulnerable to a pounding. This also works with Phantoms, which can greatly decrease their movement speed which is their main trait. Combine that with Cryo Ammo, or Cryo Blast from other players, it can bring Phantoms to an almost complete stand-still.
Arc Grenades with the electrical damage evolution and Incinerate can work wonders against the Collectors. With proper power evolutions, one can pull of 2-9 tech bursts in a matter of seconds, devastating barriers and weakening armor.
Tactical Scan, followed by anti-armor powers, is a very useful combination against Praetorians and Scions.
Spam grenades: geth are extremely susceptible to Arc Grenades and one can take out entire armies of geth single-handedly, especially when combined with Incinerate to create Power Combos. The only real threats are as always the Geth Primes and Geth Hunters. When out of grenades, try to restock when you can, otherwise use your weapons to take out the stragglers or other enemies.
There is little need to spam Grenades against basic troops since most of them will die in just one shot from a more powerful gun. Against Banshees, let rip with the Grenades and the Barriers will fall in seconds.
A combination of Tactical Scan and Incinerate can drastically weaken Ravagers, Brutes, and Banshees, especially if you've evolved the scan to decrease movement speed.
Incinerate is highly useful for Reaper forces regardless of Tactical Scan, since all but Marauders are either unprotected or armored.