I disagree with Trev -- I bought an MJ with a TrailMaster lift. The quality of the parts is decent, but it rides like it has no suspension at all, and there is zero articulation. To use the term "flex" in the same paragraph with this lift IMHO is an oxymoron.
The TrailMaster was an okay lift for the price when it first came out and there wasn't much else available for the XJ. Now there are much better choices available. The rear lift is a very thick half-length add-a-leaf, which is far from an optimum way to get lift or flex.
The one good thing is the control arm drop brackets. They hang down and can be as much of a problem as an asset when rock crawling, but for a truck that spends most of its time on pavement, they do preserve the stock suspension geometry, and that's a plus.
The kit does not, AFAIK, include any provision for brake line extensions, and you absolutely need that with more than 3" of lift.
All in all, I think I would look at Rubicon Express and their drop brackets.