The point I think people are trying to make is that LOTS of people who think they have a "shot" at keeping them -even in larger systems - do not have success. I worked with one that ate EVERYTHING, survived system crashes that wiped out far tougher fish (literally killed triggers, groupers and not the Idol), was babied, beat the crap out of any other fish put in with it, and died a year later like most do. Literally ate anything - getting it to eat was not a problem (and I often hear of cases where that is not an issue and they still die for unknown reasons). So I would truly think twice about trying. It is a fish that should, IMO, be banned from the hobby. I think you may very well waste some money.
I suppose, if you have a 30g long tank (36") and it is a small idol, and there are no other fish, then it might be OK but it is not a QT (it just allows it time to get established and not beaten up by other fish). If you have some emergency disease, you still need a QT tank.