The [Zakti] doesn't behave like usual weapons, so on paper you can easely misjudge it.
It's structered completeley like the gas damage mechanics itself (--> wiki).
That's why ~70% of the damage is in the gas explosion.
That in mind:

• You can shoot in the enemy crowd and cover all of the area with gas with just a few darts.
• Hit mobile flying enemies like Ospreys to transport your dart to the crowd
  and get the headshot multiplier.
• Shoot with it when undetected to get the stealth bonus on dart damage, gas and the proc.
• Primed fraction mods working here thrice in the damage calculation,
  make them a heavy boost and your flexible place in the build.

The weapon is designed to use the full spectrum of toxic utilty against all fractions, but also with the weak points of toxic damage. [Saryn] boosts every mechanic of the weapon like crazy.

Four important notes about the build:
1. Radiation procs are for disabeling ancients healing, the worst weakness of toxic besides armor.
In an armor-focussed gameplay, the [Zakti] is a support weapon to save time.
2. Keep in mind that Toxic Ancients are the most resistent type of enemies against the weapon. Use another one on them.
3. Saryns 3 (Toxic Lash) contributes on the dart, explosion and toxic of the gas proc.
Augmented ([Contagion Cloud]) it doubles the mechanics itself, boosting the weapon so heavy,
[Zakti] feels like it's Saryns inofficial signature weapon.
4. The mod Embedded Catalizer is in testing with [Saryn], because it could be unnecessary.
Status duration could be more important here, but work in progress in that part.
5. Fraction mods can be switched to get a more fluent battles along the fractions.
That doesn't mean you need to switch every time, but you can use the fraction mod
of your most problematic to support your melee or primary weapon.
A Riven with multi-fraction-bonus would be convenient, but WIP which kind will boost the toxin mechanic.