The military gliders made sense because they were landing in hostile territory, usually nowhere near a runway for a return trip. Those gliders were pretty much a one-way, one-time-use vehicle. I guess the Waco glider could be used to argue that towing is technically feasible, but it was intended for a totally different use case. I don't see how it can be argued that it's more economical to run, especially considering the safety issues others have pointed out.

I'm no aerospace engineer but it seems like it would be more efficient to fly one single bigger plane than to tow a second one behind it. I suppose this might appeal to certain groups where they already own a plane, and want to increase capacity without buying a whole new plane. But the idea that it's 65% more efficient just seems pretty sketch. I could totally imagine some drug cartels using these though...