Never heard of it, but have made a note to use in the future.
Recently used 2 gallons on pipe used to build fence and used to etch galvanized panels that I painted. Will probably go through another gallon before my project is done. Good stuff, but lesson I recently learned is that if the rust is pretty heavy it will come off like old paint. I think I got lucky by not having time to paint right away after using the Ospho. Had to reprep all the pipe, apply another Ospho treatment, then paint. Sure hope it took.
