If you—despite your current precautions—are interested in keeping tabs on your system’s accesses of the built-in mic and/or camera, you might want to have a look at
OverSight from Patrick Wardle’s
Objective-See. Find a recent 3rd party write-up of this free and handy little utility
HERE.
Can you explain what OverSight does that /Applications/System Preferences > Flash Player > Camera & Mic > Block all sites from using the camera and microphone doesn't do? (I didn't see any reference to Flash in your linked review.)
Edit: Is it that your camera and mic can be accessed by entities other than websites?