I replaced just the rear driveshafts on my wife's Granite with the CVD sliders, but only after I tried loosening the slipper clutch quite a bit. She still managed to pop the u-joint on a brand-new driveshaft somehow, after which I finally caved.
The CVDs have held up for quite a few packs since then, so in that regard they do seem like a worthwhile upgrade for the Granite.