I tested this mod, and it works well! The terrain displays correctly, and the player position is accurate. However, there are a few things that could be more clear:
The coordinates are relative to the holo block, they are not world coordinates as I initially thought. So setting the position to (x=1, y=2, z=3) will position the hologram at 1 node East, 2 nodes below, and 3 nodes North of the holo block.
The hologram itself only shows the highest node in a stack of nodes. So if you have a tall wall, you will only see the top row of nodes on that wall. I fixed this as a test, but it produced serious lag, so I guess it's just best the way it is.
It's unclear at times which way the holo block is facing, so I sometimes end up walking around it to see where the little red player cube pops up.
All in all though, this is a neat mod, and it works great!