I wish that people would stop citing White's page without explanation. His stuff about using known secret keys is all about IPsec. People using VPN services mostly use OpenVPN.
I can tell them one thing: use Cloak. And I know that, no matter how they do so, they won't be less safe than they would have been without it.
For more on this, see my followup to the VPN post: https://free-dissociation.com/blog/posts/2017/04/public-heal...