It's a conversion for the CJ, YJ and TJ to run coilovers up front and leaf springs in the rear. Decent idea for the CJ and YJ's, but utterly dumb for a TJ. You would be replacing coils with leaves and going back in time.
I really wouldn't want the kit for a CJ or YJ either. I believe that if you are going to have leaves on one end of a Jeep it is better to have them on the front for handling reasons.
Maybe there is something else to these new kits I'm missing, but that is what I read about them the other night.