The heart works roughly as intended, its there to save you from having to go back to your crystal every time. While I guess there are probably balance issues, The running back and forth is pretty tedious and I wouldn't want to keep doing that mid game. The requirement to avoid being hit I think makes it fairly balanced, it can't replace potions or other healing trinkets for that reason. Maybe I guess if the delay was a little longer or the recovery rate was a little slower...
Though honestly I'm not familiar with how it functions differently on Torch Bearer compared to the other gods, so maybe I'm way off topic.