In regards to my personal experience - I did 90% of the install in my garage with friends, had a shop complete it along with other repairs that were needed on the XJ.
I then had BRUTAL bump steer, had one specialty 4x4 shop look at it, they sent it to a place that specializes in front end work, and he said the steering specs were WAY out. The camber/castor were completely off, and that's wht we had to buy adjustable links, and at least one other component to get the specs back in line.
And on a more basic note, the kit did not come with some hardware, I had to source that locally.
The actual manufactured components (links, trac bar etc.) seemed beefy enough for my tastes, I was more dsappointed in the total package, and the need for so much adjustment and additional components when I thought I had bought a complete kit.
I think the lack of replacement nuts and bolts for the rear bothered me the most. Small cheap parts (from a mass-production point of view) that ended up costing me an afternoon, and about 50 bucks.