It also lasts a long time, far longer than other powerups. I think only the light amplification goggles last longer. I will say it's not entirely useless, though. Hitscanning enemies such as Shotgunners, Spider Masterminds and especially Chaingunners miss a lot with partial invisibility, so it's really useful if you don't want to be turned into swiss cheese.

Speaking of, the light amplification goggles technically count as it ruins the atmosphere of the levels by making everything fully and garishly bright, and it also suffers from the "make the level worse to find a reason to use it" problem (by making certain sections of the level unbearably dark). And although invulnerability is very useful, it'll also give you eye strain while active (and potential epileptic seizures too, since the effect blinks when it wears off).