IntelTechniques:

I have always preached using your own domains for all vital email. Sure, we all have burners with various providers for all of the junk, but I would never use a Proton Mail, Tuta, or Fastmail domain for anything which is important to me, such as a financial institution or work communications. ANY service could shut down or kick you out tomorrow. When you use your own domain, you can easily forward it to another service within an hour.

The post also stresses that redundancy is also important:

I maintain a paid package through Proton Mail, Tuta, and Fastmail at all times. I can store all of my domains at any of them whenever needed. While I doubt any of them are going away any time soon, I have redundancy.

I have paid email accounts at both Protonmail and Fastmail. I’m glad I do.