Privacy

One test I'd apply to any new private-mail provider before moving anything important: how easy is it to leave? Check whether you can export the whole mailbox in a standard format (mbox/EML), whether there's IMAP/SMTP access or a bridge, and above all use your own domain. With your own domain, if the provider gets bought, enshittifies, or deletes your account for inactivity like someone mentioned here, you change the MX records and you're gone in an afternoon.

Given how young it is and the security disclosure back-and-forth above, I'd keep it to low-stakes mail until it has a track record and an independent audit.