Not arguing with ya'll, but Fail2Ban is still being updated: https://github.com/fail2ban/fail2ban, I wouldn't call it inefficient, but I can see how CrowdSec has an advantage; because if 1 million agents report back, their network would globally block an IP address across 1 million servers. It's a little like Cloudflare.
Fail2Ban's prime purpose is to locally scan logs for patterns and perform an action.
Even though CrowdSec looks nice, it's not a local thing, the logs are sent to their servers. That's not a bad thing depending on the logs however, I have clients who would be cautious with sending that information to a third party.
@AdamM, do you use CrowdSec on any of your Enhance installs?