I agree with this - unless you have a single item that almost fills the cargo bucket, panniers are fine. Most cargo bikes I've seen don't have any more carrying capacity than a regular one laden with panniers. It's like truck vs. estate or something - sure there's some added convenience, and it's easier for single big things, but is it worth the specialised vehicle if you have/otherwise need (people capacity, maneuverability, whatever) the other one anyway?