Mendeola and VW transaxles were designed to be used with axles using CV joints. Because of this California Performance recommends using CV joints on all applications to take advantage of the original design intention.  Off-road applications with higher angles than OE applications, typical in many long travel cars is even more reason to utilize CV joints in the driveline.  California Performance cannot stand behind the usage of U-Joint style axles. We have seen failures that we believe are associated with the use of U-joint style plunging axles that include damage to final drive flanges, side covers, differentials and side gears. That said, we have heard there are people using U-joint style axles successfully.