One additional u-joint (which is never put to the same angle extremes as the knuckle joints anyway, so should be less likely to fail because of that).
The beam pivots have nothing to do with the strength of the shafts or diff, though I do tend to think in the case of the D44 TTB, the beam housings are a bit less sturdy than the round tube structure of the straight axle version. Though this isn't something a little plating to box the beams up can't fix.
i agree with what is said in this post-i've never had the middle joint fail,just the outers.shafts are the same strength on the 44 as the solid axle.beams can be bent if they hit something hard,but they won't break in half like many solid axles i've seen after jumps.that said,the arguement is apples and oranges.mud bogging or extreme articulation i would go with solid,blasting dunes or high speed off road of any sort that will swallow up lots of travel,the ttb will give more travel with less modification than any other ifs,and a better ride than solid axle.if jumps are involved,the solid axle needs a lot of trussing,which adds weight and decreases clearance.the very spot the solid axle likes to break is where the pivots are on the ttb.comes back to the hammer and the screwdriver-use the right tool for the job,one is not inherantly better than the other.