And even if you do have your own domain (I do), for one-offs these services are still useful, since they're not relatable to you, and motivated spammers can't just guess new addresses for you. For example, y'all can send me an email at [email protected], but if I get lots of spam there, I'll disable it and you'll never know what other Firefox Relay masks I have.
That, and the UI for disabling masks is much easier than having to create a new filter.
- Fastmail masked emails (https://app.fastmail.com) - Firefox relay (https://relay.firefox.com/) - SimpleLogin (https://simplelogin.io/)
There's many more.