Just got an onn pro and have found that it will play all cable and streaming channels (mpeg-2 480i/720p/1080i, h264 720p/1080p, h265 4k) except for the 1080i/h264 channels I get through my HDHRPrime/Verizon FiOS (ex. BBC News, C-SPAN, BeIN Sports, Turner Classic Movies).
My channels server starts remuxing them but the screen stays black with no audio. The onn is on the latest version of the app and the server is on yesterday's pre-release. The logs look the same as when I watch one of those channels on my Hisense Android TV which handles them with no issue.