It is maintained by Google and the whole go community since it is in the standard library. So, I think it is fairly secure (probably not as well tested as OpenS

It is maintained by Google and the whole go community since it is in the standard library. So, I think it is fairly secure (probably not as well tested as OpenSSL but the attack surface is smaller, bugs and security risks are still there, though). What is important is that the library is not hardware accelerated and it thus uses a software accelerated AES cipher. So, I think it is a bit slower, but you would really have to measure it yourself. Upgrading your Load balancer should not be that hard, though.