Some of my Bulk Rail Loaders are working for ore, but the ones for other items are not.

Check the mod setting from inside the game (Esc -> Settings -> Mod settings -> Map) and verify that the BRLs are set to allow either “ore+plates” or “any.” The option from Main Menu -> Settings -> Mod settings -> Map affects only new games. To change settings for an existing map you have to do it from the in-game options menu.

Bulk Rail Loaders are too slow. Can they be made faster?

Bulk Rail Loader speed is increased by completing stack inserter capacity research. You can increase beyond the base game limit of 12 by adding a mod such as Move Full Stacks or Infinite Technologies. This can be very useful if you're running with a set of mods with very large stack sizes.

I'm a mod author and my mod adds items I think should work in Bulk Rail Loaders. How can I do this?

During your mod's on_init and on_load event handlers, use remote.call as follows:

-- call either of these during your mod's on_init and on_load event handlers
-- takes the exact name of an item
remote.call("railloader", "add_bulk_item", item_name)
-- takes a Lua pattern (https://www.lua.org/manual/5.2/manual.html#6.4.1)
remote.call("railloader", "add_bulk_item_pattern", lua_pattern)