I like the idea of the 3' side flag as an informational, awareness event. IE, all cyclist in the city using it one day.
However, it seems a bit cumbersome for every day use to me. It'd be in the trees on the MUP, dragging on one of the bridges. It'd be pointless on the bike lanes and narrow downtown streets. Only on the two-lane road in suburbia would it be an advantage - for me.