Okay so I heard about this post but I didn't think it was real.
AirShield has some major disadvantages in a fight on account of it requiring you to stop moving and start crouching, which goes against airbending mobility styles. However, at the same time, the move is extremely powerful, as it blocks nearly all moves, and those it doesn't you can jump over.
I wouldn't use AirShield in a fight since I rely quite a lot on my passives compared to the majority of airbenders, but I would in the event that I was pinned into a corner cause with this one move I can hold off a small army and be totally fine.
It's also one of the only moves that protects against FireBurst and cannons being fired at you, which is quite something