Actually the problem with radius arms is that they want to twist in opposite directions when flexed. The trackbar defininitely causes deflection in the bushings, but that's why we run bushings/joints/etc. The opposing tension and compression from the twisting motion of the radius arms is what eats bushings and joints and can rip brackets off the axle.
With that said, the RE kit is a very good kit and has a proven track record of durability. They have been around longer than all of the other brands, and it's still popular for a reason, because it works. In my opinion, a 4 link doesn't drive and handle as precisely as a 5 link or radius arm setup (one with a trackbar). It has to do with forces and angles, but basically the trackbar works directly to keep the axle in line, while the 4 link relies on the same 4 control arms that also control front to rear position and axle torque. I'm sure now someone will come along and talk about how great their 4 link is, but I've got a worn slap out Teraflex 5 link longarm on my TJ that still runs down the interstate at 80mph no problem.
