This decoration was a gold drop in the Strategy Alliance Pack (December 8th, 2015 – January 12, 2016) and was bugged at release. It was fixed on January 12th in Patch 4.0.4.
The Massive Artillery Turret decoration is now functioning. it is a centerpiece hook.
When first released it was undefined in all fields. It could neither be previewed nor used to learn the decoration.
Bioware is aware of the issue (see the dev post here), but there has been no announced timeline for a fix. Since they have announced that they will not be addressing an issue with nightmare mode loot drops until patch 4.1 in February, I am guessing that this decoration may be unusable for some time. I’m very much hoping that I am wrong because that would be an extraordinary length of time to leave some of the current game bugs unaddressed.
The Massive Artillery Turret can be traded and sold on the GTN. The price has fallen drastically in comparison to other gold decoration drops while it’s unusable. If you feel like gambling that it will be fixed and will become an alternative to the Massive Anti-Air Turret, you could build up a nice nest egg.