My old detector was a Fisher CZ-3d and looks similar to the ATP in size and the way it breaks down. With my CZ, because it was small enough to fit in a carry-on sized bag, I chose to keep it with me and not leave it to the mercy of baggage handlers ( again because it was really not big enough to warrant a travel case -overkill as BVI Hunter put it ). I had one of those small, light weight, $60 5" travel scoop that came as well. I broke it all down, wrapped a dishtowel around the control box to prevent scratches, put that inside the 5" scoop for protection, and then fit all the poles and other supplies around the bigger pieces. I kept the batteries out of the box, but kept them in the bag in case the TSA people wanted to see it turned on.
To my surprise I never received any grief from the TSA people and I carried it this way for all my trips up until last year when I got a new detector.