It never caught on because you loose a cog space with the device. Mid 70's spacing was generally 126mm for 6 speed and with the Porta Catena you would only have room for 5 speed. Bianchi changed their spacing on the Specialissima frames to 130mm in the late 70's early 80's to accommodate the device AND 6 cogs but it wasn't sold as OEM equipment on complete bikes so it didn't get the traction it needed.

vjp