As far as odea is concerned, I think it can be the plural of the greek odeon and the latin odeum, or concert hall, which was derived from it. So maybe I should have said plural of odeum in my earlier post. It may be a bit obscure, but it's not technically wrong.
As for "not half", surely leaving half of "allo allo" out is the same as just having half of "allo allo". And using the phrase "not half", meaning "I should say so" makes the surface reading of the clue much better, and more natural, in my view. I'm sure that's why Enigmatist did it