Well, the infocard says it's just an old transport. A factionally-limited old transport (only IDs which allow liners/slave liners). I don't think anyone in Sirius would manufacture a liner for the sole purpose of hauling slaves, not even the Outcasts, so I don't think that it's a problem.
I can't speak for everyone here but a lot of ID's limit ship types to certain smaller classes, and then the liners. Prison and Slaver. The biggest of which is the Slaver.
The Junker ID for example states you can use Fighters, bombers, GBs, CAs, BBs, Slave liner, Prison liner and the Salvager.
Transports and trains?
For some places, the Salvager just doesn't cut it with just six guns. Shame really. I think the potential was great but compare the Salvage Frigate with a Pirate Transport. 150 cargo units more, a lot weaker defensively. Maybe the 'Frigate' should be a Frigate and get up-gunned?
Make it an option that has certain 'appeal'?
I think that Slave Liner is transport. But he cost so much for cargo hold, so more good to use enother transport to trade. Luxury Liner I think it's small cruiser-gunboat. Have 11 guns, 220 000 armor like cruiser, but have small attack guns, because it have small level - 7.
it is a liner, an old an outdated one.
everyone whoes ID allows to fly liners, can fly it.
Orbital Spa and Cruise, Cryer and Planetform inc. might look a bit silly with it, but Reasearcer for example look good with one.
There are not too many IDs that allow Liners anyways (or only specific ones).
I think all Military guards should be allowed to fly them, as are the BAF Guard, since it makes e supperbe training target for young recruits.