Our thoughts on radius arm, vs. 3 link vs. 4 link. is that they can all work if they are properly designed, however different applications can be used depending on what you plan on doing with your XJ.
Radius arm. This is a tried and proven system, that flexes amazing, offers great ride quality, and is fairly easy to install because you are attaching to all the OEM axle mounts.
3 Link front. We find no flex improvement, and no ride quality improvement. This kit does use larger 2.5 forged johnny joints for the uppers which will withstand more abuse. This kit is recommend for the more aggressive driver, mainly competition setups. In competitions guys are running sticky tires, on concrete courses, using front only to drag the rear. This put a great deal of load on the front joints, and yes the 3 link will hold up to this type of abuse better then the radius arm, which uses 2 inch johnny joints.
4 link front. While designing the 3 link, we look and saw that to add the same arm on the other side would be fairly easy at this point. We figure guys doing racing, jeep speed stuff, jumping, would appreciate the extra arm with the large 2.5 forged johnny joints. This kit will most likely need some custom exhaust work to clear that 4th arm.