No repairing of scratches. There's a hard coating on the shields and any attempt to remove a scratch will rub through the coating and it will kook worse. You can get just a replacement glass for the windshield from HD that uses your existing brackets. There are aftermarket units available too but the quality isn't the same as the HD ones.
I have used that Novus #2 polish on scratches. It doesn't remove/repair the scratch but it makes is less noticeable. I have used it on helmet shields as well with good results.
Another vote for the Novus products, they really work well.