I saw the Tight Lines feature this morning, and it seemed that the bright blue toy whale and the bright yellow ball attached to the line (weighing 9oz) didn't spook the chub and barbel at all. It was as soon as the chub moved off with the bait, shifting the weight and the line off the bottom that spooked them.
About fluoro, because it's invisible (or near) underwater, when a fish rubs against it they can feel it but not see it, spooking them. with braid or mono which is more visible they know it's there so when they rub against it they won't be spooked!
There was a lot of really good info on this programme, especially the tidbit about chub "crunching" when feeding, which attracts the barbel in. They share a swim as well, none of this barbel bullying the chub out. There were little minnows swimming in between them as well!