I got a Tab S3 2 days ago.
I've tested with MX PLAYER all heavy HEVC HDR videos, 10 bits UHD 2160p @60fps, and of course all other formats and bitrates.
EVERYTHING WORKS GREAT. All in HW or HW+.
Even the AVC h.264 UHD 2160p @60fps "Big Buck Bunny" works perfectly and fludly in HW+ (jonathonalexander told it didn't work fluidly???).
This Tab S3 is a must!
Also tested European version of Galaxy S8 with Exynos 8895 and it's able to read excatly the same video files as Tab S3 with absolutly no jitter.
Both Tab S3 and Galaxy S8 claim to work HDR file formats and it's true.