Q1; There's a Rzeppa style constant velocity joint inside the ball housing, same type of joint used for the outer joint on todays halfshafts found on most fwd cars and IFS 4x4 trucks. Otherwise, the shafts inside are the same as what you would find in any other 4x4 solid axle. The Rzeppa style joint allows for smoother power transfer over a Spicer style joint.
Q2; The actual hub itself isn't quite as long as it appears in the pix. Most of the length is for the spindle and bearings, which are the same as the rear full float axle. The additional length is for the aftermarket locking hubs, No real advantage, just simply the size they needed to house the components. Most newer solid axle trucks have gone to a center disconnect in place of locking hubs, plus sealed type bearings, so they do not have the extra length.