Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
On Roku devices they're called channels, not apps. The best way to determine if it's available on your device is to use the Channel Store directly on the device. It will only show what is available for your device and your location.
If you haven't bought a Roku yet, you can look in their online channel store and see if it's listed. Since even the oldest version of the Ultra is still fairly new, every available channel should work on it.