I use it all the time, it's the perfect little spell to get you out of a jam.
Just out of curiosity, I know it doesn't work if you pop before it summons the ship, but will it still work if you go above 50% before the ship arrives? Because more often then not, I end up being blown up while waiting for the reinforcements because I am not sure if I can heal safely.
i can answer this. as long as you hit the button before healing and make sure the timer has started yes you can heal. sometimes when in STFs using this i have been healed by the borg set bonus after using it and the ship still comes.