They block some tracking. What percentage of tracking they block is anyones guess. 99.999%, 90%, 50%, 10% ? Who knows.

Also, they don't block targetted tracking, which would be used by a stalker for example. They only block widespread well known trackers.

Only way to be safe is to disable loading of all remote resources and don't click links.

(Unless they take what I've discovered and incorporate it into their system. Even then, it wouldn't be 100% coverage. Some tracking links, ie. Mailchimp, can't be avoided.)