Not only is it a good backup, but a fantastic primary paddle. The reality is for most paddlers that a straight shaft is going to be the easiest to operate and maneuver with.
While a bent shaft will allow a greater stroke length than an SS, the benefit comes in a shorter stroke and a faster cadence for the non-marathon paddler - with easier correction strokes in less than ideal conditions (wind, inexperienced paddling partner, etc.) Not to mention the advantages with regards to a silent stroke and underwater recovery.
-Erik