From reading that, it lets you establish connections within your tailscale vpn. Iroh let's you establish connections between devices regardless of their network.

Similar on the technical level (though QUIC vs WireGuard), but that would make your app dependent on Tailscale, and require your users to have Tailscale accounts. You'd also be limited to Golang currently.

In theory you could run Headscale, but you're really working against Tailscale's intended design at that point, and Iroh was built for this from the ground up, so what is Tailscale buying you?