A long downhill stretch will also completely beat it (if it wants to maintain a constant speed downhill). Any flywheel or other counter-rotation system will have to keep accelerating for as long as the hill continues, or else it will tumble.
I think that is likely the downfall of this kind of vehicle. Yes, with slosh control you can make it work well in normal circumstances, comparable to other vehicles. The failure modes, though, lead to worse accidents than other vehicles, and I don't see any advantages of it in normal circumstances to counter that.
For instance, can it accelerate without gerbiling?
