A lot of the other free dynamic DNS services don't cut the mustard, or have vanished over the years. Some of them have weird rules like that your IP address has to be dynamic and change every once in a while, some of them have terrible software and don't have a clean API, some of them require you to check your email every month to click a renew button, and most of them don't have a web UI you can use to manually type in an IP address.

DuckDNS just kinda sits there and does its thing. So it may be interesting for a HN audience to know that a decent usable dynamic DNS service is still around.