I know of knowone personally that has broken the shafts themselves. All the failures I know of have been the cages exploding.
As far as the slip shaft, I see no need for it unless you have come up with a suspention mod that allows a lot more up/down arrticulation than what our stock suspention will allow (think trophy truck like 22 inch plus of travel). The green cup allows the balls/cage to move about 3 inches to keep the length in ckeck.
I really like the option of being able to replace the ball/cage with a heavy duty option...that would be the route I would be interested in. I have 2 factory and 3 Empi shafts that I can use! The cage removes with a lock ring...pretty east to do.
And again thanks to all that are getting this rolling