The cloak works somewhat. im using the 1.6.1 release of MC Eternal, which uses version 1.4.2 of constructs armory. i have a farm for wither skeletons that i was testing the invisibility on and the results vary from i can walk in between skeletons, to mobs aggro to you anyways just ignoring the cloaking effect. I have tested this with/without trinkets, only chest plate or full tinkers armor (chest plate only seems most consistent with mobs not attacking). however most of the time the invis effect is really weak with the mobs staring at you then 1 out of 12 mobs locked in a room randomly detects you and attacks while others don't do anything.

is there a way to strengthen the invis effect to make mobs not detect you period, so it has some use for modded servers? for pvp, its not really useful as there's mini maps that show the players location anyways