Series II lift question?

Hello all, firstly thanks for such a great site, I've learned/used a great deal of info here. So, here's my question. I'm looking to buy and install a 3" lift on my 2000 classic xj. I've searched so much my eyeballs are on fire. I've seen the RC series II lift contains lower control arms, where the Rustys does not. Can you explain why you need/don't need LCA? I'm leaning towards rustys 3 AAL lift. Thanks-

well to start they are a lot stronger and will allow for a larger tire size too.