Fortunately, composite materials tend to disintegrate quickly to red-hot powder once broken, instead of large chunks of high-velocity shrapnel.
There's also anything built in layers, where the outermost layer will shred, bleeding off massive amounts of energy in relatively low-mass pieces, much more easily contained. Often carbon fiber, but that's just the main material I've seen for this. Dangers associated with flywheels are becoming less and less of a problem, and will only continue to do so with more research.
That said, I'd still be interested in seeing how it reacts to a hard collision. I think that quote mostly refers to over-spinning.