I am using a hero point in letting the players roll a second d20 and add the roll , meaning you can use it to turn a good roll into a spectacular mostly crit success. So this point is truly heroic instead of using those points in not failing which is to be honest less epic.
It might happen that when you use it for a failed roll you might add only a second miserable roll , if thats the case ... well even heroes fail.
But when you need to kill your nemesis in one hit and you roll a 17... you
might get lucky with another 18 for a total of 35 .. crit happens.