This is the second limit break of Rinoa, accessible once you acquire Rinoa from space. So when you enter Ragnarok and fight the Propagators, then you can use this limit already. Since Combine isn't accessible at the Ragnarok part of the story, this is the only limit break you could use while in space. Though once you've come back to Earth, Rinoa could use both this and Combine.
When this limit break is activated, Rinoa would levitate and wings would sprout from her back. Once she descends, you wouldn't be able to control her again until the end of battle or until she gets KO. She would continuously cast magic which inflicts 5x more than the usual damage. At this state, she wouldn't be affected with some status ailments like Silence, Confusion and Berserk plus her MAG stats would be maxed to 255. If you want to control Rinoa again, either just let her be KOd then revive her using Pheonix Downs or Life magic or cast Break to petrify her then cast Esuna to cure her. Take note though that if Rinoa doesn't have any magic in stock that are allowed to be cast during her Angel Wing state, she'll just continuosly do physical attacks to the enemy which is similar to the Berserk status.
One point to take notice here is that Rinoa wouldn't cast Curative and Support Magic such as Cure, Cura, Curaga, Protect and Shell. Instead she'll use offensive magic that range from weak ones such as Fire, Blizzard, Thunder to strong forbidden ones like Ultima, Meteor and Holy. Keep in mind that she would only use magic that is available in her inventory. Also that every spell she casts really isn't deducted from her inventory.
Tip: Here's a small tip. Angel Wing has the capability of being a more effective limit break than Lion Heart. How? Keep all the Curative and Support magic such as Cure, Cura, Curaga, Life, Full-life, Esuna, Regen, Aura, Double, Triple, Float, Haste, Protect, Reflect and Shell for junctioning purposes. Then remove all the Offensive Magic from Rinoa's inventory and that includes Elemental (Fire, Blizzard, Thunder, Water, Aero) and Status (Bio, Death, Confuse, etc). Now, as for Forbidden Magic, the only one that you should place in her inventory is Meteor so that that will be the only offensive magic that rinoa will cast. Notice that Meteor deals multiple damage to all enemies. and so with Rinoa's maxxed MAG stats, Meteor can deal 9999HP damage at least 6 times. If you boost Rinoa's speed stat then she'll be casting Meteor spells one after the other.
Looking on Squall's limit break Lion Heart,after the trigger play, it still isn't sure if Squall will do a finishing move. If ever he does one, there's still a small chance of him doing a Lion Heart especially if Squall has learned his other finishing moves. And so that gives Squall a slim chance and a small probability that he'll do the Lion Heart making Angel Wing a more effective and more reliable limit break.