If there's compression of the wheel/spokes/hub etc then this can reclaim that and return the power to the wheel, but it won't create any new power the rider didn't already put in, or that gravity gives you going down a hill. So for example any spoke flex or rim deformation is lost energy to us; you'll get almost none of it back. The stiffer one's wheels, the less loss there is. Normal wheels and this wheel both don't get back anything from the tyre.
So I think the comparison should be between a modest non-racing wheel on a city bike and what this does. What it might be is a more efficient wheel than a mediocre one, but not by much. However if you bounce your bike then it might work out as an amusing way to get down the high street.