I wanted to try it out just now but hit a roadblock immediately - it cannot automatically obtain and maintain TLS certificates. You have to use an external client (e.g. acme.sh), set up a cron to check/renew them, and poke HAProxy to reload them if necessary. I'm way past doing this in 2023.
https://www.haproxy.com/blog/haproxy-and-let-s-encrypt
https://github.com/haproxy/haproxy/issues/1864