IMHO... AAL or Shackle for a lift is like asking Synthetic Oil or Dino Oil as in it can get very passionate.
The philosophy I use is the following.
If the ride is how you like it now, the Shackle is the way to go. I'm not convinced that shackles cause springs to flatten out faster. We used War-153 shackles on a set of OME-36 (2" lift springs). Those springs start out soft and we put upwards of 200k miles on them before I had to do work to them. That includes 4 miles of dirt road every day (it was the DD for many years), lots of freeway miles and some good hard off-road.
Over time the springs did get flatter and the rear suspension was softer than I wanted. I then took a leaf from old f-150 spring packs I had around the house and replaced a leaf. (Its been a while, now, I'd have to "count" to see if I replaced or added).
The new/extra? leaf stiffened the ride a little and brought the back end up another inch so its right where we wanted.
Now, if you don't like how it rides now (too soft) and it is too short, the AAL is the way to go..
A full set of springs is around $400 (I think its actually less).. ARB USA (aka Old Man Emu or OME) makes a 2" set of springs for the rear of the X. They are softer than stock but for off-road that is better. For towing or sport type driving, that is not better.
~Mark