Umbral Facade

In normal space, not Untethered, head to Shadow Point and run near any of the mobs with Shadowguard in the names, including the Menders on the outside, then click on your item. You do not need to have them targeted, you just need to be in proximity. I was able to run into a pack of them and get 3-5 done at a time, then kill the pack. The Menders seem to give 2 credits.

You can do this in the untethered space (phasediving). Just use the Essence Scanner before you kill the mobs. No need to target or attack them, it's enough to be in proximity. You can scan the mobs while being in stealth/camouflage.

Just to reiterate you need to be in MELEE range (more than likely in combat with them) to use the device; you can't use them at range.