The first being you can lift and shift to another email provider very easily.
All alias providers I have seen (including SimpleLogin) allow arbitrary target/"backing" mailboxes.
just get a domain with alias provider and it matters not what email provider you use ever.
Personal domains are nice for "important stuff" that should be tied to your real person.
One of the features of mail aliasing services is it to provide pseudonymity which you cannot achieve if the domain literally contains your real name.
They do but it's a limited kind of alias. You can't set up reverse-aliases (you send first) for example which the regular SimpleLogin can.