Every Android device has issues it just depends on:
a) what connected Audio and Video equiptment you use and
b) how fussy you are about picture quality, particularly 1080p > 4K upscaling for the video purists.
c) which Android Apps are needed and actually work on tablet Android or Android TV.
d) if you need working Kodi PVR's and deinterlacing.
If you wanted Kodi 4K HDR - which in reality is not full sorted out yet on AMLogic Android Marshmallow, even with MINIX Firmware - and Kodi HD Audio - then the U9 would be the tablet Android device to get.
But where is the properly encoded, convenient & easily accessible 4K HDR video content ?
- in 4K Android TV Netflix and Amazon video servers that only the nVIDIA Shield can access.
HDR is nothing more than a media player technical wankfest unless you can get hold of properly encoded HDR content with correct HDR Metadata.
IMHO the actual best bang for the Android buck currently for (non HDR) tablet Android is the hybrid - AML S905
WeTek Play2.
Because it is not just a one trick pony, but can run 3 different OS's easily. vs the U9-H - A bunch more easy to use Android TV Apps work on the HDCP 2.2, DRM, Netflix Approved - Play2. Even when using the tablet Android OS. Play2 downside, no Wireless remote.