I think this is the epitome of a "one-of" card. It's effectively a "First Aid" for a Hero, and it gives them a higher cap of health. Being able to put it on someone else is just icing on the cake. Low & high health Heroes alike benefit from this card.
Play under any player's control. Max 1 per player.
You get +3 hit points.
This is a solid vanilla card that I think is worth the cost, and if you are playing with multiple people, then adding a couple in allows you to see yours earlier if you need it and hand one out to someone else to make them feel safer as well. It could mean another round in their hero form they wouldn't have been able to do otherwise and of course you now have a new health cap.
This card, like Down Time, is a game changing card that becomes one of the primary generic power ups alongside Avengers Mansion and Helicarrier (though obviously less powerful and cheaper). Any character whose design is limited by not having enough hit points can take this card to fix the problem. Examples include Ms. Marvel herself (her recovery is too high for her hit points) and Spider-Man (not enough hit points to take full advantage of Aunt May's incredible healing power), or really any character with only nine or ten hit points who wants to avoid suddenly and unexpectedly dying.
Even if you think of this card as a healing card rather than a statistic boost, it is still clearly pretty solid. It gives three points of healing for only two resources, which I would consider to be an acceptable rate of return for something that only works on identities, with the advantage that it can heal you even if you aren't wounded, but with the disadvantage that it only works once on one character, which isn't really a disadvantage if you only put one of these in your deck.
When you play it, do you get to add the +3 hp right away or it only raises your maximum? Also, if you are at 2 hp and you lose this card, is your character considered having 2 hp left or he goes to 0 hp?