I see so the only difference is that they provide 600 aliases on their domain compared to lets say 25 of other providers. I wonder how they deal with poluted namespace.

So It so different from random domain catchall?

The reason why i would be worried about Fastmail is that they have are Australian company with servers in US. Both of those mean that Law enforcement can simply ask for users emails.

Now i am for sure not target of Law enforcement or goverment so i dont care but i am not sure why i wouldnt use service thats in better juristiction and is privacy focused.