Half shafts with U-Joints vs. CV Joints

According to Carroll Smith in one of his books he stated that combining u-joints and CV joints was definitely not a good idea. He much prefered the CV joints and gave the tip of using the zip ties around the boots to keep them from expanding. On the halfshafts that I have worked on, the inner joint usually has slotted tracks for the balls to allow for the in-and-out movement of the shaft during suspension travel. On halfshafts with splined joints the friction on the splines as the parts slide puts a load on the joints on either end. This occurs mostly during acceleration. On the Datsun 810 halfshafts that I worked on they used splines with a radius and had ball bearing in the splines between the two parts to reduce this friction. I think the same thing was done on the Z cars with that suspension. I have seen u-joints break, but usually something else will go before a CV joint comes apart.