OK...the one piece cam will either grab both ropes simultaneously and work perfectly to secure the footlocker, or will fail on both ropes simutaneously if the cam fails for some reason (only scenario I can visualize would be loss of the pivot pin). Since the latter could conceivably happen, I think a backup via a friction hitch on both legs above the Shunt, or a mechanical like I described would still be a good idea.
Smaller diameter ropes might escape the Shunt...I'm not sure about that, but if possible then again it means a backup is imperative.
On the surface of it, there may be no more risk than using the R.E. dualcender (alone) like Greg advocated in the original linked thread.