Not sure what's come of it since their cert at https://youi.tv is broken at the moment.
My experience with it was working at a big tv network who was trying to port all of their native tv apps over to this platform.
From what I recall:
It was a pain for designers because they had to retool their Sketch workflow to Adobe After Effects, which nobody liked. The idea was that the designer would design the view layer in AF and pass it along to the dev for integration. In retrospect, I think this was a mistake: developers should have been doing that from the beginning, as the workflow was similar to VBA or Storyboards and required intimate knowledge of how the view would be integrated into the code.
Most developers who worked with it loved it or hated it. It bridged the gap between platforms, but came at the cost of losing out on unique native platform features without writing complicated C++ bridging code on each platform.
The idea sounds solid at first, but you're really just trading one massive problem for another.