The entire premise of Tailscale SaaS builds on creating tunnels around your firewalls, then enabling the user to police what is allowed to be routed through these tunnels in a intuitive and unified way.
Headscale seems to have nailed down the part of bypassing the firewall and doing fancy NAT-traversal, but can they also fulfill the second part by providing enough of their own security to make up for anything they just bypassed, or will they descend to just being a tool for exposing anything to the internet to fuck around with your local network admin? To me, not giving your Tailscale implementation any way for the user to understand or veto what the control server is instructing the clients to do while also not auditing your servers code at all sure seems daring…