In a way, this is like another copy of Armored Vest because for each time you defend you eventually heal (instead of prevent) 1 damage. With Aerie, though, you count Defense events too, not just basic defenses. This makes it better in the Flow Like Water archetype or any multiplayer deck that plans on defending for multiple players.

The other really interesting thing about this card is that you can save up all the counters for one or two bursts of healing in Alter-Ego during the game. Decks built around defending a lot usually want to stay in hero form as much as possible since you generally have no way to defend in Alger-Ego. That makes this a preferable healing option to Crew Quarters or Down Time, for example, since you don't need to plan on flipping down as often as possible.

These types of strategies work much better in multiplayer than in solo, but the Aerie is definitely worth an inclusion in the defend-a-lot decks for a huge burst of healing at fairly low cost.