I'm currently in the process of trying to get as firm of a grasp on ephemeral beings as I can, and in the process of cataloging them for the sake of myself and my friends, I've been intrigued and puzzled by Goetia.
The major hang-up I'm having with them is that they possess no Manifestation abilities and have to be provided them by the mage. I've been reviewing the book several times to try and get a solid idea on how mages would do that, with the Bind Spirit, Revenant, and Familiar spells having various options, but Goetia don't even possess the Twilight Manifestation on their own.
What happens to them when the spell runs out and they cannot maintain any manifestation on Earth?
In the Astral Realms, sure, there's no problem, but with no means of manifesting on their own, why would Goetic Summons mention the Open condition? It's all very confusing.
I wish the book was more clear about this. The ephemeral system was already a bit of a chore to learn and these guys are giving me a headache. It stinks, considering how fun the concept of summoning characters from the public eye to fight on your behalf is.