One of the references gave an interesting fact. No throttles accessible to pilot or co-pilot. The engine controls were the function of the flight engineer in the room behind the pilots. The crew operated like a surface ship- the Captain called out the throttle positions needed, and the flight engineer operated the twelve throttles! It is a good thing it was a seaplane- must have been hard to set it down right on the numbers, with the pilot not having access to the throttles! And, moving all those throttles must have made chopping the throttles take more than an instant in time!
Dornier built three, and two were actually operated by Sana, the Italian airline. Later taken over by the Regia.
"and two other machines based on orders from Italy – the X2, named Umberto Maddalena (registered I-REDI), and X3, named Alessandro Guidoni (registered I-ABBN)."
That's the one I chose to do, per the classic old Matchbox 1/144 kit.
-Wiki.