Difference in their features. FAQ manager plugin has less options than Knowledge Base Manager. Unique features that only available in Knowledge Base Manager are –

1. Live AJAX search.

2. Sticky Buttons for user question submission and live search panel.

3. Responsive grid system. You can display your questions in 1/2/3 columns.

3. Related Knowledge base questions.

4. Up and Down voting system for your KB contents and user able to submit their feedback, if they found KB contents are not useful.

5. 3 type of widgets to display top liked/top disliked/featured/popular/recent posts.

6. Extensive option panel to customize everything.