You can't make it anywhere other than Cerys due to it requiring the Fulgoran Cryogenic Plant, and it's kindof a waste to simply burn it in heating towers, so clearly it's meant to be used as a train/vehicle fuel elsewhere. Except, it's really annoying to ship anywhere since it has a stack size of 1. It does have a massive 5GJ fuel value, so I suppose that's still reasonably dense, but... plutonium 238 is also kindof rare? I suppose if you shipped plutonium-239 out and used it for energy in mixed-oxide reactors instead of the vanilla ones you'd get more than the standard amount from the Fulgorian reactor...

Has anyone gotten use out of it?

The stack size of 1 is not really appropriate for a space-transportable reward, so v4.18.0 changes it to 5. Otherwise, yes, many players use it for trains.