Just depends on the tank. I did one run with pretty much the worst tank ever (ended every fight with full MP, never flashed) and we died several times throughout. Did 2 more runs with magnificent tanks and the final fights were a bit hairy but still pulled through without deaths.
The final fight isn't a cake walk and the roaming mobs make it interesting if you don't know their paths. I like it, the instance itself is pretty cool, like a big haunted house.