From my understanding, the point of an air dam is to limit air going underneath the vehicle, directing it around it- which is why they usually have splitters. It seems that a design like this would send considerably more air underneath the car than a vertical, or even outward projecting dam. I would make an educated guess that this is better than no air dam at all.
Keep in mind, the further out you extend/lower you drop the air dam, or air splitter, the smaller your safe approach angle will be. One reason lawn edging it a preferred tool, it is cheap, firm but not completely solid, and like my old air dam, it grinded down to the perfect height for my commute.
This car will never see a speed bump:
