I haven't seen that many people get this (seems like the mission is bugged and won't drop it, so caches only) and for this reason there isn't a lot of media on youtube. For those who are interested, here's how this thing works:
The debuff part is pretty much a carbon copy of Predator's Mark - land 10 shots without switching targets and you apply Disrupt instead of Bleed. If you hit another target it resets the counter. The counter for the stacks shows up in your buff bar, not on your gun like with PM. The Disrupt seems to be guaranteed, but I have not tested this against other players so I cannot confirm whether it can be resisted. There is no animation or spool up, so it's just a Disrupt that is applied out of thin air.
The damage bonus is the interesting part. It doesn't work like Sentry or like Striker.
The stacks are not applied to the target like the Sentry 4pc, they are instead applied to you.
Stacks do not "over stack" - after 10 stacks it resets and you will deal extra damage equivalent to stack count *2. So basically maximum damage that you can get from this holster is 18%. After that it just start to cycle through the damage bonus...
BUT the stacks are not removed when switching weapons, like they do on Striker 4pc.
AND the stacks will not be removed when shooting a different target with a different weapon. I.e. you can build up 9 stacks, switch weapons and enjoy 18% extra damage unconditionally for the next 20s.
Comments and Speculation:
The last detail allows for some silly stuff - the holster works extremely well with the newly released 93R, which is 3 round burst. 3 full bursts in a target will retain the 9 stacks and give you 18% damage, after which you are free to switch weapons. With the new Skull MC Gloves this will allow HE builds to get some high base weapon damage modifier pretty effortlessly. The stacks last for a whole 20s, so IMO it's not too much trouble to to build up to 34% damage before Tactical Advance and Competent+Booster Shot.
The Disrupt is pretty bizarre. If you hated the Bleed in the DZ, this will just crush you. On one hand it's a bit too strong IMO, particularly because it has no range limit. If it was casted in a fixed radius around the user then maybe it would have been a bit fairer because then the victims would have had a chance to get out of range of the Disrupt. On the other hand it's a needed ability - FA is ubiquitous and groups with dedicated medics are tough to take down. This is the hard counter for all of it. It makes Ballistic Shield users a serious threat, not just because of the damage, but also because "tanks" can now lock down healers, skill users and all of their fun toys. Maybe even push people to start using cover.
AMA