It works fine. We went to hit Guardian of the Seal, who's down in the same area last week. I just stood at the edge of the pit, and invited 5 people at a time, letting them hop off.
The 3-min only recast on Invuln makes it quite handy, compared to 15 mins for the Cleric version (I assume the Pally is the same, dunno about Necro). At the end, I even invited a few who could DA themselves since they were still sitting there waiting for their spell to pop up. Got the whole raid down there in 15 minutes.