Yeah, I tried that for a while, and I have some Apple generated forwarders too.

In the end in places like a store that wants you to sign-up for X% off, or something it's easier to just to give them [email protected] and see what happens.

It's actually pretty low friction in terms of management.

As I said elsewhere in the comments here, I didn't like the [email protected] format of masked emails because if you're using a custom domain and you have 200 logins using masked email addresses, then want to change your email service, you have go through those 200 services updating the email address for each one. I'm trying the same setup as you suggest above on the basis that Fastmail allows you to block specific email addresses in case you start getting lots of spam to a specific address through the catch-all.

Yes, custom domain future proofs it. You can route that domain’s email to any servers via MX records.

I have put in some blocks before where services don’t let you unsubscribe.