It's hard to appreciate On the Brink with the current card pool, but if you are playing with everything you have this cards gets ludicrously good very fast. It completely outclasses upgraded Unexpected Courage. Having this in hand means you can take bigger risks, and commit more cards in hand to a test you want to pass without worrying about wasting all those card if you draw the wrong token.

This especially helps you a lot with skills that care about succeeding to trigger, like Do or Die and Resourceful, and especially cards that want you to succeed by 2 at least, like Brute Force, Sharp Vision and Expeditious Retreat, while also offering autofail protection, letting you return the card and draw one to replace On the Brink.

It has less good synergy with Take Heart, given you usually want to commit this to test you know are gonna fail, and getting a +2 makes said failure less certain, outside of Drawing Thin, but the level 0 version introduced in Miguel's pack works a lot better for that on the basis it only gives just a +1 instead.

So if you are a Survivor that likes to commits lots of cards, like Silas Marsh and Isabelle Barnes, there is no reason why you shouldn't run this. You won't regret it.