I disagree with the advice given here - even the reference for the accepted answer concludes:
You can of course use query string parameters with HTTPS, but don’t use them for anything
that could present a security problem. For example, you could safely use them to identity
part numbers or types of display like ‘accountview’ or ‘printpage’, but don’t use them for
passwords, credit card numbers or other pieces of information that should not be publicly
available.
So, no they aren't really safe...!