I have a TJ and will be lifting it in the next few weeks. With the "Belly Up" skids as stated before it changes the vertical distance the Driveshaft has to go. To do it correctly I have seen that most people go with a SYE (on the 231J) and a CV style driveshaft so that it can flex more. That also brings up other issues with the Rear Axle since you need to get adjustable control arms to and adjust the shock mounts.
I have been trying to work out a list of items that will accomplish what I want , done correctly, with Dirk at DPG. He has been very helpful and pointed out many things I didn't think of or find in my research.
As for XJ's, I am not sure how much of a difference you will notice for the extra items it will add to your list (CV, Control arms, etc). It might be more worthwhile to get a different skid that doesn't move the TC, but has a trail side that has fewer things to catch on. That TNT one looks like a good deal. Of course for TJ's since THEY are overpriced...everything else has to be. Not sure if you have both a XJ and TJ like I do, if you do I have a 03 TJ and would be happy to tell you some of the other things I have found would need to be done.