I am now on a Lupine tour in March 2025. Even though it was not on the schedule, five of us payed extra to get here and we're taken there by Bassie from Lupine West Africa +232 76 947442. From Freetown it is more than an hour on a speedboat (what the locals call a speedboat, just a bigger dingy with a Honda engine). You go up on Sierra Leone River, passing by the ferry loading, passing by a railroad that ends up half way above the river and it is used by Chinese to load the iron ore. Then passing by Tasso Island, much bigger and full of locals. 

Arriving at Bunce Island, we had a vivid tour (almost reenactment) describing all the atrocities that took place here. Even without a guide it is easy to identify the ruins, the gate of no return etc. But there is no signage besides the ones at the pier and the ones by the wall pictured here. We had a 75 minutes intense tour, some people surely could do it in 30 minutes. There are also some impressive trees. There is a newish building apparently built with money donated by Colin Powell in 2002 for a library/museum (it was closed, nothing there to see). There is also a cemetery on the other side of the island. I doubt there is any effort to pursue a WHS nomination, even though my opinion is that this certainly deserves it. There were two old men volunteers who took some money from our guide, he knew them by name, they supposedly protect the site.