Fury Brand is obtained by using Breath of the Earth six times. Aeris can equip the Cover Materia to speed this up, allowing her to fill her Limit gauge faster by receiving more damage. Using a Hyper on her also gives Fury status that boosts the pace a Limit gauge fills. A good place to grind Limit levels quickly is the large forest in the Nibel Area past Mt. Nibel. The Battery Cap enemies here are fought in large waves and their laser attack can increase Aeris's Limit gauge quickly, while the Valron fought there has Gravity-based attacks that can increase Aeris's Limit quickly without killing her.
Fury Brand fills the Limit gauges of the two other party members fully, allowing them to instantly use their Limit Breaks. It is preferable to save Fury Brand until the other two party members' gauges are low or empty to optimize its use. Because Fury Brand effectively amounts to using two Limit Breaks at once, it is a very powerful ability, making Aeris a strong supporting character. Its usefulness depends on the strength of the other party members.
Fury Brand can also be used when grinding Limit levels. For many Limit Breaks, obtaining the next level requires using a Limit Break many times, a process Aeris can greatly speed up. This means that Fury Brand remains useful throughout the game.
Fury Brand remains useful in certain situations over some of Aeris's level 3 Limit Breaks. If other party members' Limit Breaks are set to level 3 or higher, they will charge their Limit gauge slower than Aeris, meaning she can allow them to perform Limit Breaks more often. Additionally, when grinding to improve Limit gauges, Aeris should continue to use Fury Brand to the benefit of other party members. However, as far as Aeris's defensive Limit Breaks go, her level 3 and higher Limit Breaks are more useful overall.