May I ask why? What are the benefits of HyperApp over mithril?

Hyperapp looks like it'd be a pain to use for anything other than small widgets.

I'm asking why you prefer hyperapp because Mithril has router and xhr capability built-in, and hyperapp doesn't seem to have those features. But hyperapp is really tiny though. :-)

There are addons for routing and HTTP requests for hyperapp, and they add trivial amounts to the bundle size.

The reason to use hyperapp IMO is it is far closer to the actual Elm-style FRP model, and as such includes functional state management out of the box, in a far less awkward and boilerplate heavy way than Redux provides.

Because HyperApp also has state management built in.

If I understand correctly, HyperApp enforces the so-called SAM pattern, but that's it. Calling this "state management" seems to me an exaggeration. And why would one use a view framework to do (domain/application) state management? It doesn't sound right.