Have never seen these TA curved cranks before. They look remarkably similar in pattern to a steel cottered crank that Fred Grubb use to fit to his top of the range tandems in the 1930's. Think these steel curved cranks were also French made. None of us can remember the makers name and we had a Grubb Pullman with them on. My Dad sold this in the late 70's complete with these unusual cranks. Someone on the list probably knows what they were called? There is nothing new and most of this gimmicky stuff had been tried prior to World War I.
Best wishes and be lucky. Michael Butler Huntingdon UK.