It's mildly useful for hauling loot and providing some support firepower at the same time, but dies as soon as it faces a ship that knows how to fight back. Unless you manage to capture one, I would never waste logistics on fielding these.
But I think the idea for these ships is that they are going to be like the Peasant converting into Militia in Warcraft III - sort of lacklustre military muscle for when you desperately need it, with the potential for clutch plays. So basically, when the campaign starts to resemble its final form, maybe you will be building some freighters on one of your outposts, it gets attacked, you have the option to try to make 4 buffaloes into buffalo IIs and a tarsus into a Condor and you can try to throw a defense against the attacking fleet.