I'm ok with loot-boxes in paid games if they are purely for cosmetics.
It's also a bonus if these items are then sell able (on the steam market place for example.
I've gotten lucky and opened chests that contained items worth hundreds of dollars. (which i then sold to buy more chests)
Things like character unlocks and gear upgrades are taboo though, unless its a f2p game.
I agree, nothing wrong with it as long as its purely cosmetic unless of course as you mentioned it is f2p. Spot on sir!