This set ignores all LoS and as along you are somewhere nearby, even you are as far as max Snipe range, this set will sniff you out. Let me present some cases:-
Case 1
Was solo-flagging a keep. Got it to 55%, till 3 magplars show up. Before they could reach me, I get off siege and sneak. These guys reach my siege. They set it on fire and throws a few shards around hoping to hit me, but I am a totally different place. Then, all three change sets and equip Internal Guardian and start spamming Annulment. Immediately the ground under lights red and being a vampire magblade, I manage to move away unhit but guess what, even though it says "Hidden" on my side, I am instantly subjected to 2 Soul Assaults and 1 Cheese Beam.
Case 2
Around 30 guys were PvDooring a keep. My small group of 4 arrives sometime before inner FD falls. We decide to flank the guys from stealth, but guess what, 3-4 guys wearing Infernal Guardian spamming shields and even before we reached nearby, we are all revealed. Two of us got Tremorscaled to death by nearby Stam-Sorcs and StamDKs and the other guy got beamed to death. I managed to get it with 2k HP left. But wow, the moment I get in, even before I can move, wondrous balls of fire comes flying in through the door almost magically and finished me. I notice that half of the inner guards are already dead from this stupid set.
People are totally ignoring tactical skills like Magelight and Revealing Flares or even AoEs to use this broken set to easily find all enemies without even doing a single thing. Every zerg seems to have a few exploiters dedicated to shield-spamming with this set to sniff out all opponents. This is getting more and more ridiculously as many players have started keeping a IG set just detect enemies cheaply. As if Cloak was not broken enough already, ZOS had to make this gem.