I have one of their's that can connect to your phone. It's not needed, it just adds extra cook book functions. It even hosts it so you can control the sous vide when you're not at home, almost like a reverse proxy.
But yea the physical buttons work fine without the app.
My car works fine without a seat warmer, but if you sold it to me as part of the car then later it started charging me a subscription I'd be pretty pissed.