Well, optic orbs typically remain [i]invisible[/i] as the spell, unless they attack for little damage, after which they have to use a swift action to reinstate the effect. In addition, [i]see invisibility[/i] and [i]true seeing[/i] typically only have an effective range of 120 feet. But then, the optic orb's ability to examine magical auras using its [i]arcane sight[/i] ability is limited to 120 feet as well. The optic orb's Darkstalker feat, precludes the use of blindsight, blindsense and tremorsense as a means of trying to locate it.

It basically serves the same function as the protoss [url=http://starcraft.wikia.com/wiki/Observer]observer[/url] unit from the Starcraft games, except it uses spell-like abilities to augment its sensory and stealth capacities.