I tried this, but the thing I didn't like about it was that it ties you into Fastmail. I like using a custom domain so it's relatively easy to change your email provider, but masked emails are in the format [email protected] so you'd need to revisit all of those accounts if you want to change your email provider to someone else. I'm currently trying using a catch-all with [email protected], and will be interested to see how much extra spam comes in through the catch-all.