The standard Web Shield is always running and giving its protection, that doesn't change (unless you have disabled it, not a good idea).
What the AOS add-on is doing is giving you advance notice in your browsers web searches and more detailed information when you visit a site, should you choose to visit it (as in the AOS link given). Or if you have arrived at the site from a different link than a search.
Personally I feel that having chosen to visit a site that has a poor reputation from the search results is a bit late to be gathering details on its reputation.