There are lots of size 6 creatures the Eater would be terrific against. Unfortunately, those will most probably avoid direct combat, and instead send smaller Bane Lords or Wights to do their bidding.
tested it with patch and its no good for 50 astral...30 seems about ok as a price.
that it goes independent makes it unique, but destroys the unit kinda. by the time you can cast it (conj8) you can win the game in many other ways. and this ione just is thorn in your empire sooner or later. why pay for it?
lol, no chance i could see it, it attacked 6000 undead when i tested it, would be more user friendly, if it would not attack the province first it came from, but rather a province next to it. And maybe some AI to protect its own existence too.