Does heads ale replace DERP too?

Headscale does have a built-in DERP server, and you can run standalone instances using code from tailscale (there are a bunch of docker images you can find on docker hub, or you can build one yourself), which you then have to include in Headscale's config. I've done this for a while, but I was running into connectivity issues when on the go using a mobile connection, so I've been falling back on Tailscale's instances for now. I should try again sometime.