If you have a domain where those drawbacks aren't showstoppers, you might also look at Yandex hosted email. Can't beat the price (free), it has decent storage (10GB) and the limit for sending is 500/day[1].
Those drawbacks are also valid for any other small provider. Fastmail also has the problem of mails classified as spam. Really any service except the biggest 3-4 have occasional reputation problems.
The difference is just that Migadu is honest about it.
Would have not expect you to change either. Fastmail is awesome and a lot of respect for them. We're trying to learn from them all the time.
I'd classify Migadu in a different category. If you run multiple projects or just need extra addresses fast at no extra costs, you'd probably not go for FastMail. I can clearly see using them both.
I'm happy with Fastmail, but Migadu's pricing is very appealing...