Yeah, breaking one on the trail would not be a fun time.
However, if you think about it, you pretty much have to strip a knuckle to get a shaft out, taking the knuckle off wouldn't be that ridiculous. I would think that it'd pretty much destroy the knuckle and C if the bell exploded though.
The shafts are 35 spline 300M so I would assume they'd be comparable to CTM's junk. However I've never heard of anyone even breaking a Superior shaft, much less a CTM shaft. Time will tell, I'm not ready to overhaul my axles yet so I'll see how the tests go.
One other nice thing about these is turning radius, if you can clear your tires, these will turn a lot sharper than u-joints.