I have read through some of the literature on this forum on both of these types of water supply. From what I have read the F&D is better than the constant flow floating beds according to Oliver. He does not specifically say how the floating beds were fabricated. I am going to make some assumptions here.

1) the F&D allows the roots to access oxygen when there is no water
2) the CF has a floating bed with the roots of the plant dangling in the water supply. Systems I have seen in pictures show the bed above with the water supply underneath sort of in an enclosed space. If the roots are entirely (or mostly) covered in water the only oxygen they will get is from the water and not the air. Even if they are not covered with water the gaseous oxygen in this enclosed space would or could deplete to some extent causing a deficiency?

If the floating bed was raised to allow air circulation or the floating bed was fashioned so only a portion of the root stock was touching water and the air space below the floating bed was open to atmosphere (not a sealed bed on top) would this not work just as good as the F&D?

Without doing any calculations it would seem to me that energy wise it would be easier and less expensive (pumps & energy) if there was a slow controlled flow over a flood type of system, especially if the tanks being used were somewhat on the same level with each other.