After decades of solid research, mostly led by Robert J Englar, why is Circulation Control, the Circulation Control Wing not in use at all?
Circulation may be controlled via either air blown through spanwise slots or horizontal-axis rotors, alone or in combination.
Experiments on wing systems go back at least as far as 1902 and since then almost every variation imaginable has been tried.
The problems come in the engineering implementation. Where investigations have reached the stage of flight testing, and in many cases sooner than that, the conclusion is always the same. Either you have a system of large air ducts threading through the wing structure and weakening it, or you have a spinning rotor to support along the span of the wing. Either way, the wing must be strengthened and that means more weight. Both approaches require a supplementary power source, more weight again. The mechanical complexity compromises development time, manufacturing and maintenance costs, and reliability. The thing may work, but the downsides of the weight and complexity are greater than the benefits; the technology is not cost-effective.
So I am not sure what evidence base there might be for claims of actual weight reduction.
If you really want super-slow flight technology, get a helicopter with VTOL thrown in for free or, if you are rich and desperate for somewhat higher speeds, a V-22 Osprey.
Who knows, the balance may change as technology advances, stranger things have happened.