Would love to understand it better too. It looks like the use cases are similar but the tech is different. NetBird is an alternative to Tailscale that uses Wireguard under the hood while these seem to use Traefik under the hood.
Pangolin is "public ingress to private networks" and not a mesh VPN/network builder. As you say I think NetBird is an alternative to Tailscale and we are an alternative to Cloudflare tunnels, Ngrok, or Zscaler. It is more about exposing things publicly with authentication in the browser for people to access than about building a network for disparate devices to communicate.
It is correct that pangolin is something like pinggy.io or cf tunnels as you mention. But those do not give such fine grained access control it seems - like a firewall checking identity and all.
But definitely it is not a vpn or mesh network it seems.
https://github.com/netbirdio/netbird