[Autumn]

What concerns you regarding it?

In that most mages will more than likely taking all the ranks into invocation so they'll never fail an invocation, and the thing Devocation did before was make it so that you wouldn't really 'likely' fail any invocations upon being hit, I could see devocation making the user gain an armor/magic armor buff equal to half your scaled FAI, but only when casting mercalan domain invocations.