Use with any sentinel companion to get an extra 15% chance of upgrading critical hits to the next rank (yellow to orange, orange to red)
You can further increase your upgrade chance by using Vigilante Pursuit on a Warframe and/or [Vigilante Supplies] on a primary weapon (preferably put these in exilus slots)
This build also helps against single targets to reduce armor and slow if they aren't immune.
I kept [Rime Rounds] unranked to balance the two status effects and proc them both equally, it also happens to save a Forma because of it :)