What I can find on "Hey" so far looks extremely basic as far as UI goes.
And by all means, if what you're building only requires a very basic UI—absolutely go for it.
My argument is that when you're faced with is an intrinsically difficult UI problem, React (or similar FRP-inspired frameworks which the community has stabilized around) is a huge improvement over the "simpler" past way of doing it. And the only way to really understand that is to try building non-trivial applications with both.