I think you misread my comment. Apart from the UI polish, I wasn't impressed --> I was impressed with the UI polish but less so the rest.
I'm aware that implementing this well is a difficult problem and I have utmost respect for those who figure out how to make it feel seamless.
It sounds like you underestimate how hard it is to have "UI polish" implemented just right so that it feels seamless and natural instead of a hack (because honestly we do love to hack but ultimately prefer our prototypes to be implemented first-party, e.g I've been using JACK to stream audio in sync on various devices for years but AirPlay is so much more simple and natural)