False, it only gives you one last chance. More dangerous and even less effective than playing one Miracle or some healing spells.
The problem does not occur in the magnitude of the damage/healing.
The problem is, you will only use it in two situations :
1.You can win the game if opponent receives 40 damage
2.You will lose the game if you do not get 40 healing, and that extra 40HP can help you win the game.
Now you can see, this card is like " 50% to win this game"
Miracle is more powerful but the fact that it's not probability based makes it acceptable in the game.