Not OP but I do both. I pay for a fastmail account and have <myname>@<one of their domains> which all my _personal_ things go to and then I have my business emails all route via their Aliases and certificate pointing.

There have been some instances where both the fastmail domain and my business domain ended up in Spam for the receiver but that is less than a handful of times and I used Fastmail via Nodemailer as a proof of concept for a newsletter service so (ab)used the service without any issue.

I use both, but also pipe in gmail to ensure I don't miss any emails during what inevitably ends up being a long transition process.