I just put one on my 7120. It definitely adds some bushels and allows for longer passes and less wait times for the truck. My impression of it is that it works, but could be made stronger. I put it on myself and it just seems that there should be more/stronger attach points to the existing top. There seems to be lots of them out there so they must work. I doubt it would fail but at the same time would not be surprised if it did. I think the metal rods you are referring to are the ones that go in each corner to act as a brace for the rubber. I think there should be 2 per corner and that you should attach the new rubber to the old rubber too. Make sure if you get one you leave enough space when you drill your holes so you can fold the new topper down. I made the mistake of being a hair to low and now I can't fold it in. Overall I think it is worth it if you find yourself often having to wait for trucks to get back.