Worked in exploration for me; got a trade route coming into Daegu worth 18 gold, after slotting the tradition I got extra production and food to match:
Some thoughts, now that I finished antiquity.
First off, I did not appreciate how Sangdaedeung (the merchant) works - I thought it's a minimum of 5 gold when neutral, and then 10 at friendly and 15 at helpful, but no, it's +5 per a rating point. That means that at the maximum relationship (90), plopping down a trade route generates 450 gold. Combined with the diplomacy points they can put out, and the extra trade range and resource slots they get, I was happily spamming the routes to every allied settlement and city state I could find. I ended up with 37/20 economic score as a result, four well-developed cities, five towns with all the warehouse buildings, and the highest combined gold, science & culture per turn I've seen yet (though playing science Himiko definitely helped with those, too).
Secondly, this was definitely the best case scenario I could have - I shared my continent with Ibn Battuta and Jose Rizal, both extremely easy to befriend, so after disposing of a couple of naughty indepent powers, I could ignore military development completely and focus on city building. I feel they need that kind of start, because best parts of their kit do not carry over; automatic trade routes between capitals, extra trade range, extra slots in towns are all crucial to making their kit work, so you need to get a good starting state into exploration, cause the actual traditions won't help much. They're a bit like Normans in that regard.
Thirdly, their unique district is excellent, both in terms of the results and in the requirements - getting a spot that's both rough terrain and surrounded by mountains or natural wonders is far from guaranteed, so it pushes you into some interesting decisions. Do you want the extra resource slot, or the extra influence? If you don't have the mountains or wonders, how much adjacency can you generate with wonders? It feels nice to play it, given that influence is the reward. It also makes getting spots like this feel really good:
Lastly, they will be very volatile civ to play, I reckon. Relying not just on getting lasting alliances, but also alliances that result into trade routes beyond antiquity, is very finnicky - but if you can get them, that extra food and production can really superchange you. On the flipside, if you find yourself on the receiving end of a warring neighbor, there's very little to help you. So still no idea how strong they really are. But they are fun.
