It is pretty good, but it’s not an “SSL” config generator; it’s an “OpenSSL” config generator. It only supports OpenSSL. No GnuTLS, no NSS, nothing but OpenSSL.
Specifically it's for Apache/Nginx/HAProxy/AWS ELB which link against openssl (there's also a node port). Are there alternate bindings for any of these for GnuTLS, NSS, etc?