Do you mean it works reliably well in letting users through, or in blocking AI?
Both, check out this article talking about it: The Day Anubis Saved Our Websites From a DDoS Attack
Looking at the statistics really shows how dire things have gotten with AI crawlers. The before and after is crazy. There are some other blog posts also mentioning they get maybe 1000x less requests per hour after deploying Anubis.
It's not a big deal since git repos aren't hard to migrate. GitHub is fine currently and if they push people away then there are a couple of alternatives.
Firefox hosting on Github is a good move because it lowers the barrier of entry for contributors.