TT isn't a tracker, so it's not public or private. It's an aggregator that makes it easier to find things from Nyaa, bt.edwardk.info, Anirena (well, when it was up), and all the fansubbers' personal trackers. That's why it lists broken .torrent links from sites that have since died.
Personally, I use AniDB for notifications, then use TT to search for the particular file I'm looking for, as its usually faster than going to the fansubber's site and scrolling through releases I don't care about.
Some people lurk in #news and pay attention to release notices in there.