Flyertalk is deliberately blocking VPN traffic with Cloudflare, it isn't difficult to identify VPN IP addresses as most households don't have thousands of simultaneous connections to HBO or BBC iPlayer.

It comes down to why you're using a VPN
Start at 6:08

If you need the anonymity of sharing an IP address with so many other subscribers that disaggregating your traffic is nearly impossible you're further ahead with a commercial VPN.

If you don't just roll your own OpenVPN server with your very own IP address that will probably fly under the radar, although some websites block the IP ranges of cloud providers to block data miners.