You can forward mail to/from gmail with it basically the same, it has a very low sending limit on the free plan (but I'm not sure if that applies to mail forwarded from gmail), and it claims to attach a footer on the free plan (like forwardmail.net does), but it doesn't actually seem to do so to mail forwarded from gmail. https://www.migadu.com/en/guides/gmail.html
Meanwhile it has it's own webmail/pop3/smtp servers so it will be easy to move away from gmail entirely in the future.
I also just really liked the tone of the website, I have a lot more confidence in them not doing scummy things than I do in forwardmail.net not doing scummy things (though that is just based on reading a website, not the most reliable indicator ever).
Anyways, we will see in a few months if I think I made the right choice.