I don't know why someone said useless, but it does have that pesky kernel driver bundled, and it's in perennial turmoil. When it goes bad, it goes very bad, and it's impossible to predict when it will due to system differences. I know that they're in the middle of development for a major new version that will include a completely new driver, one that they expect will largely solve the problem, but that's a ways out and it's unproven at this point.

doesn't AdGuard let ads through that pay to be let through?

Yes, because it's a trash can, not trash can't.

Braves ad blocking shields are their own implementation separate from extensions. It won't have any issue continuing to work.