Hello,
1) It takes one second to enable the option during the product adding. This option was integrated to highlight new products as by default recently added products are shown first.
In addition, this feature allows filtering this kind of products in the Product Grid and Product tab. So there is no other option to add new badge without having to check the option.
2) Yes, you can use brands inside a mega menu you just have to edit the relevant html block and use the brands element inside it.
Best Regards.