Streamed it first to see if it was worth buying on disc, it is.
They have a really cool commentary feature where the image is shrunk to a 4:3 image so they can split it top and bottom.
The top image is the film as presented, the bottom image is the raw footage before visual effects were applied.
It lets you see how much of the film was digital and how much was practical. Complete with commentary.
It's only on the Blu Ray, the 4K is only the theatrical release.
Ok, thanks! I think I will pick up the "regular" blu-ray then, this extra sounds really intriguing!