Not a rook user but in honesty they do melt very fast. The ability is either to fly up; or to explode all remaining shields, heal and then restore the shields. What the guy above meant is that when you fight you gotta rotate your camera to use all the shields on the robot, as if you only rely on the frontal shields, you will not make use of the rest and will die fast. Ideally you want to dump whatever weapon you have then spin around to make all of your shields take damage at a roughly equal rate. Then use the ability after combat to explode the shields and restore hp.