Avtomaticheskiy Pistolet Stechkina – ★★★★ Handgun
Or Stechkin for short. Good RoF buff. Actually combos nicely with other RoF buffs if you need more since her aura shape isn't as weird as Calico's. Works EXTREMELY well with IWS. Try to grab her unique equip, it helps.
Having Stechkin allows you to put a different HG in position 5, whether it is K5, Grizzly, Mk23 or even M950A for the double ROF buffer (for FP RFs).
Five seveN is almost always better, unless if you are not running crits at all for whatever weird reason (low ROF ARs at night), or if you already have max crit for some other reason. That being said, Five seven is not always obtainable.
Overall a solid unit.
What more can I say? Just don't slap her in echelons randomly without thinking. ROF cap is a thing. Also note that she cannot replace M950A/Astra if your position 4 is already occupied by something you cannot replace.