Seem to remember this from my old WWII comics, wasn't it called a krummlauf or something?
Didn't work very well in the 40's anyway. Would think torque produced by the rifling would lead to all sorts of interesting groupings.
It's a funny looking thing, is that actually a second weapon in the flexible bit? Can you fire them simultaneously? And surely the crossways recoil will be progressively worse the further around the corner it points?