I am a BT Sport subscriber via SKY who has Apple TV 4K and a Roku Streaming Stick+.
On reading this article, I upgraded my subscription for the extra £5 per month to see what the 4K picture looks like. I must say I am rather impressed, was watching Rugby and I'm not interested in Rugby but the picture quality and streaming was of such a high clarity I was immersed. I think this is a good move by BT Sport to have their service on more platforms. It is a pity there is not more 4K content.