Here's a response from our Lead Engineer, Eric...
"Judging by the original sample bar that was sent to us there are a few factors that work together to cause these to fail. The first thing is the surface finish is terrible. The second is there is what seems to be no effort to stop corrosion. There's a very slight chance it might have been plated originally, but if it was, the rust had already won and it would only be a matter of time till it broke. The third reason was the heat treat hardness (ultimate strength) was a little lower than you'd expect for that part (if you assume it was going to be made out of 4340). Now we didn't test what the material actually was but whether it was 4140 or 4340, the strength was lower than they could have pushed it to.
So on our bar we fixed all three of those problems. We centerless grind them to a 32 rms finish, we make them out of 4340 and heat treat them to a ultimate strength that's roughly 25% higher than the original, and lastly we finish them with powdercoat to prevent corrosion.
As far as the design itself goes, its really not that aggressive because bars that are really long and thin have lower stresses. Even with this bar going all the way to 90 degrees the stresses are a little bit lower than the what we see in most of our VW torsion bars. It's actually pretty clever because the packaging of that torsion bar is a lot easier and gives progressive resistance whether your closing or opening it. I can't comment on the rate and whether its too stiff or too soft because I've never opened or closed a flip pack, but to get the same affect with some sort of gas strut supported mechanism it'd be a lot more complicated, expensive to make, and hard to package.
-Eric T."
Hope that helps!
Best,
George K.
Sway-A-Way