https://vpntesting.info/ I tested 29 Windows VPN clients for DNS, IPv4 and IPv6 Leaks. Six (AirVPN, FrootVPN, IVPN, Mullvad, Perfect Privacy and SlickVPN) performed perfectly. Three others (CyberGhost, oVPN.to and SecureVPN.to) hit VPN-specified nameservers directly while reconnecting after uplink interruption. But that's not a huge issue, in that they didn't hit other nameservers. The other 20 Windows VPN clients failed in various ways. Over half leaked IPv6 packets whenever the machine was connected to the Internet. After uplink interruption, some failed to reconnect automatically, and some leaked IPv4 packets.