I had a game recently where I got backpack drones on my UEF ACU. They were useful, but a little later in the game my offensive ACU was almost always in range of enemy AA/interceptors.
The drones would get built and then immediately vaporized creating a constant eco drain for no benefit. It would be nice if you could toggle the autobuild for them like you can for the backpack TML. You could even re-use the same button since they're mutually exclusive upgrades.