I've been using https://www.ssllabs.com/ssltest/analyze.html for years now. Any major benefits to either of these?

I started using testssl after first using slabs.com.

As the other commenter mentioned, testssl.sh lets you can websites that aren’t public yet e.g. test environments or other private networks. As well as testing against starttls if you need to test encryption on a mail gateway.

It’s also configurable, meaning you can have it test tls protocols alone, or ciphers alone, client renegotiation alone making it quicker and easier to read if you are looking at specific areas

testssl.sh allows you to scan stuff inside private networks, supports custom ports/SNI, and things like StartTLS.