No idea, the only thing I've used my coins for is some of the legacy unlocks.  Which you have to be careful because some of them are like $5 for a 40k unlock and others are $2 for 500k.  I also realized too late I could have saved a ton of money and time if I had used it to buy the grade 7 ship packs, because grinding the same few space missions for two months to get enough commissions to buy them is a big fat NOPE.  The whole system is confusing - it seems most of the rewards come from random packs?  And then they offer specific packs that change every now and then?  Whatever, I only have like 500 coins left.
I also squandered an embarrassing amount of credits on character perks without realizing I was in the character-specific section.  Shit like bonus xp and getting mounts at lower level is PER CHARACTER, wtf?