Im not sure if its because the spy addon is getting updated with more features, but to me it´s almost like a wallhack.
Its incredible powerfull towards ceartian instance entrances that located inside with lots off passageways, and after having used it for a week I can say there would be people i wouldn’t have found without it.
now it only show people that are within vision range, but the biggest advantage comes with places with lots of walls and corridors it still show up on spy even if you cant see them on screen.
another good point is an easy way is to decide with enemy class to CC in open world pvp with your friends, and who to focus down first easily providing the enemies class and lvl when you click on the icons in spy. (spy is usually bad at figuring another faction player lvl until you click the icon)
I recommend everyone on pvp servers to try it out, it becomes quite obvious when you follow someone in ghost form to see who else is using it, and even if it feels like cheating, the more common it get the better.
Know im sure alot of people will still refuse, trying to hold a higher integrity of fair play and whatever, but its just a game, don’t have to use it to slaughter others, more of a heads up.
Since its quite a shame to miss out on something that can be so helpful, your just giving away an advantage to someone else that happily slaughter you trying to get into a instance.