[noggin]

Beware - I'm pretty certain the ODroid C2 is an S905 not an S905X box - so has zero support for HDR.

I hear HDI and 10 bit mentioned a lot in the context of some players not handling 4K bluray rips.
I need to read up on whether its actually a big issue.  

If you only want to watch regular Blu-ray HD movies - then HDR and 10-bit support are less of an issue.

If you want to watch 4K content - then a large proportion of this is sourced from UHD HDR Blurays which are HEVC/h.265 10-bit and used HDR10 - and thus HEVC/h.265 10-bit HDR10 compatibility is required for playback of these.  If you only have an SDR display, then you also need a platform capable of playing 10-bit HEVC/h.265 HDR10 content AND tone mapping it to SDR. (Without this your content will play, but the content will look totally washed out, desaturated and 'flat')

Another format that is around us h.264 10-but (h.265=4 Hi10) This format isn't used in consumer content, but is popular for fan-shared anime. It's not a format that is widely supported for hardware decode (*) - so most platforms have to software decode it, which means a more powerful CPU is required than for other codecs that can be software decoded. A couple of very modern multicore ARM SoCs now have enough CPU power to do this for 720p and 1080p h.264 Hi10 content. (Apple TV 4K, ODroid N2 both seem to)

Beware of confusing HEVC/h.265 10-bit hardware acceleration support (which is now widespread) with h.264 10-bit hardware acceleration support (which is not widespread)

(*) Some Rockchip SoCs DO support h.264 10-bit hardware decode - which caused a bit of a surprise in the Kodi community.