Tailscale is built to be global to your device, while iroh is built to be embedded into each application. This allows application developers and users a much more fine grained and bespoke setup, than having a single global bridge.
you can embed tailscale on the application level https://tailscale.com/docs/features/tsnet
you can embed tailscale on the application level https://tailscale.com/docs/features/tsnet