Pretty self-explanatory really, the spell is an otherwise guaranteed infiltration spell.
Unless you close a door.
Unless you move faster than the eye can travel.
Unless you don't meet up just to talk spoilers.
Allow me to point something out-
There is currently no way to detect the eye.
Not even for folks with GSF abjuration or the rarer ARCANE DEFENSE DIVINATION.
There should be a way to detect/counter the eye and I think it's just easier to incorporate it into the the already existing WARD AREA spell.
There are very simple ways to avoid Arcane Eye and it is detectable.
It is extremely tricky to use and thus probably about balanced.