Yup, but in all cases the currency will be responsive to the aggregate economy, not the local economy. I'm not very knowledgeable about African economics, but

Yup, but in all cases the currency will be responsive to the aggregate economy, not the local economy. I'm not very knowledgeable about African economics, but that said, I think that the downsides to a common currency experienced by Greece will be a much smaller issue in Africa, because stability is more important than monetary policy tools and "natural" inflation during debt crisis. The monetary solutions (market and/or policy solutions) just aren't available to most of the smaller African economies anyway. OTOH, currency stability is a problem and common currency generally helps with this.