But the big problem with non-native VPNs on Mavericks (by which I mean, any VPN which requires installing additional software beyond what is built-in to the OS) is that they tend to bypass any HTTPS proxies you have set up. Without an HTTPS proxy, Mavericks will have trouble connecting to most servers because SecureTransport doesn't support modern cipher suites. In e.g. Firefox Dynasty this won't matter since it ships its own (modern) SSL implementation, but Apple Mail (for example) will be unable to load most remote images.
This is why I have the note about privatevpn on the website—it took me a bit of searching to find a service that was low cost and supported a Mavericks native VPN protocol. I don't really "trust" any VPN service, but they're useful in certain specific situations.