You can correctly argue that it's balanced cost and DPS wise against other units in the game. Like BRINK explained very well in this video on air units here. I'm not debating that so do not start foaming at the mouth just yet.
I want to talk about the airspeed of the unit. Especially in relation to larger maps and teamgames. The Restorer is slower than the T3 gunships of every other faction that has them. It's the slowest flying unit in the game at an airspeed of 3 - 8 according to the unit database here.
Low speed is a serious weakness for a unit with a designed AA role because:
1. you can't react to incoming threats quickly enough (use ASF instead);
2. it's impossible to pursue an enemy air force that will outrun your forever (use ASF instead).
If you want to attack land targets (emergency defense, or simply on offense) or navy you have the imo better options of T2 gunships, Mercies or T2 / T3 torp bombers respectively. For offense they are not the greatest either because everyone with half a brain will spam flak in the sight of gunships. This reduces the Restorer to a stationary defense role. A flying SAM turret with +50% mass cost and + 800% energy cost and less than half the DPS. Conclusion: just make SAM's instead.
So my question is how do you use the Restorer? What is the practical use of this unit?