This is the main board of the BEN and, if you compare it with the picture here, you will see that it's exactly the same circuit board as the SJ Econet Bridge. The difference is that the second of the two Econet interfaces, on the left in the picture here, is not fitted, and the Nexus interface on the far the right of the board, is present.

That clears up a little mystery as regards the SJ Econet Bridge for me!