How effective is ProvaDent for maintaining healthy teeth and gums? Is using this superior to brushing and flossing, or able to add extra protection that is meaningful?

This is not the most powerful means to ensure healthy gums and teeth. It is a nice marketing story, presented powerfully and in an effective fashion with the visuals, but it is overreaching and has some liability in the bargain, primarily, in suggesting that all one needs to do is use that product to have healthy teeth and gums and that is not the case.