I have played several skirmishes just testing out units, and of all the "special units" i find this the best. So long as you have the power to build it and ssutain the -5k energy each shot, its worth the investment. Two of these can oblitorate a base in minutes. Just make sure you dont have an army near by as the shots will continue to land even once the building is destroyed. Dont want your units dying from "friendly" fire.
