My naive understanding is fastboot actually understands stuff like your client-side routing, and how an Ember app 'loads' and fetches data (from your API) so you don't have to recreate that stuff with duplicate code on the server-side like you would have to with the aforementioned React example, and I think, your library.
i think it heavily depends on how coupled your router is to your view and data/fetch layer. with domvm everything is decoupled, so wiring any of those modules up is pretty trivial.
a more fleshed-out demo would be valuable for a more realistic comparison. they mention the non-congruence between ajax vs node's fetch, but this is easy to shim so the same code works on both.
the main complexity is the view rendering and post-render hydration.
