LPT: If a site doesn't accept alias sites like Simplelogin, create the account with a disposable email site then change it to your alias
I just did this on a website that said my Simplelogin alias isn't allowed for signup, but changed it successfully after the fact from a disposable email.
You can also buy a custom domain for a few bucks a year, it gives you more control over your email addresses and is unlikely to be disallowed.
Depending on who your email host is, your domain could get blocked as spam.
Having never used Simplelogin, if I sign up with them and use an alias to send to my actual email address, do I still use the actual email client? I assume the answer is yes, that Simplelogin just provides an extra hop between sender and receiver. Or am I oversimplifying this?
Yes. You still use your normal email client. The only time it gets a little weird is when you want to send an email from the alias. You have to use your alias provider's app or manually splice together the to and from address in a specific format.
Email aliases are totally worth it though.
Yeah pretty much, its a way to sending and receiving emails without giving out your real email address. Instead you give aliases than end with "@simplelogin.com", to protect your privacy and which are then forwarded to the email you provide to simplelogin. The received emails have a different sender address, for instance instead of forums@macrumors.com, you see: the forums_at_macrumors_com_randomcharactershere@simplelogin.co.
You can actually reply to forums_at_macrumors_com_... and simplelogin will forward the email.