The Roku Ultra (Click here for pricing on Amazon) is one of the first streaming media players out there that supports 4K HDR but you need to make sure that the 4K TV that you want to connect it to also supports 4K.
The Hisense 50H7C 50 Smart 4K Ultra HD Ultra Smooth Motion 120 LED UHDTV claims to support HDR but during its initial release it could only play HDR content coming from a USB drive (and not from a HDMI connection). Click here for Amazon Pricing on the Hisense 50H7C 50 Smart 4K TV.
Since the Hisense 50H7C 50 Smart 4K TV does not yet support HDR over HDMI, the most benefit you get with the Roku Ultra is to be able to use its voice control features and access Roku's superior library of online streaming media channels.
To use the Roku Ultra with the Hisense 50H7C 50 Smart 4K TV, first make sure that the TV and Roku are powered on and connected using the HDMI 2.0 port. Once both systems are on, you should see the dancing Roku logo start up.
Once the Roku home screen is up, you need to make sure that your Roku Ultra has a good connection to the Internet. To set up or check the network, go to Settings -> Network -> Wireless -> Update Connection -> select any available WI-FI Network.
Roku has one of the most extensive collection of streaming channels so you need to find and add the channels that you want to see. However, unlike other media players, even popular channels like YouTube must be added manually.