Everything depends on the special situation and application. Such general statements without knowing the facts usually are not worth much. At last they should give a reason why they dislike them.
If you mean those foam insulation boards used as duct, they sound like a good idea from a thermal and installation point. But my concern would be physical damage (poking a hole etc.) or degradation of whatever connects the pieces. If done right, and in protected location, they COULD work. But in real life, a metal duct may be more durable.
No personal experience, just saw them at an exhibition.
