That is the person who decides what to fly, when to fly, where to fly. There is no such thing as kit maker in command or manufacturer in command. The first thing we all do before every flight is decide if this flight can be done safely, which includes a self assessment of our own condition and skills adequate for the conditions.
Mr. Wachs should get at least a light sport license. Then he could legally fly any of Mark's wonderful, safe, easily-flown airplanes. If he got a recreational pilot license or a private pilot license he could legally fly a Cessna 150. He might find the structured world of FAA-approved flight school much more comfortable than the wild and wooly world or ultralight flying.
Or, if it is absolute safety he seeks, I would suggest a different hobby such as model electric trains.
Dick O'Reilly