One limitation of custom DERP is that across tailnets, they don't share the same DERP maps and don't have access to each others' DERPs.
With Tailscale Peer Relays, the available relay bindings can be seen by the devices on either side of a connection; as such it should work out of the box with a sharing relationship between tailnets.
With Tailscale Peer Relays, the available relay bindings can be seen by the devices on either side of a connection; as such it should work out of the box with a sharing relationship between tailnets.