one check
What WebRTC gives away
Two things are worth measuring here, and only one of them is usually shown. The local addresses matter far less than the comparison: does WebRTC see the same public address your web traffic goes out over?
What this one page cannot tell you
Whether a specific site would use WebRTC at all, and what it would do with the result. We also do not probe your local ports over WebRTC: one widely used checking page does, to guess at installed software, and it guesses wrong.
The interesting part is usually not a single value but the disagreement between two. The full check reads all five layers and shows you where they contradict each other.