In terms of security OpenVPN has the great advantage of providing authenticated and optionally even encrypted tunnels. It is based on OpenSSL for certification and either uses static pre-shared keys or TLS for dynamic key exchange. The use of X.509 certificates can be regarded as very secure. It can only be compromised, if the secret key is not kept safe.

The certificates are not bound to specific hosts. They can be used anywhere between any two hosts. So an owner of a certificate could put both public and private key on his laptop and with that set up an authenticated tunnel from anywhere where he has IPv4 connectivity. This, of course, is the desired functionality for any Virtual Private Network solution but in comparison to the usual IPv6-in-IPv4 tunnels this has quite a few advantages for the deployment of IPv6 on for example dial-in lines where users not usually have static IPv4 addresses. It provides the user with much more flexibility at the cost of security relying solely on the fact that the user keeps his keys safe and only uses them for himself.