I was able to test it out last night and successfully made it from Stanton to Pyro.
The tunnel is currently just a greybox/placeholder most likely to make debugging any issues easier, but the fact that their tech works is game changing.
While party jumping isn't in, it is possible to follow someone else into the jump point and if you're close enough you can see them throughout the entire jump.
Transitions are indeed seamless. I was also able to move around a ship while going through the jump... (no loading screen).
It is possible to collide with another ship/object mid-jump.
Currently there are a number of reclaimers/vultures cleaning up the exit points of the jumpgate from the collisions occurring there as well.
Also made the jump multiple times so far, when the servers were cooperating. While everything visual is pretty much just placeholders for now and it's clear a lot more work is needed, it's still very encouraging to experience the JP actually working and allowing transit from Stanton to Pyro and back again.