If you're interested in moving some apps to them as well, they do provide other interesting services (I'm using invoicing and document storage)
One of the good things I've read about Fastmail and Protonmail is they are incredibly reliable and privacy conscious. Likewise, they seem to focus primarily on email as opposed to Zoho which seems to offer a variety of services aimed at businesses. I wonder if the email service offered by Zoho for private email users holds up to that offered by Fastmail and Protonmail?
It's up to you whether you care about the extra protection like encryption of data on their servers in your use cases.