Absolutely terrible. I booked a flight around a month ago from LAX to Seoul with an overnight layover in Japan. However last week, I found that Japan had changed its immigration rules and stopped issuing transit visas. This means I was no longer allowed to have a layover in Japan. After upgrading to the premium services, (30-ish $), I talked to many agents to try to find the best solutions. Many of them were rude and none of them let me speak to their supervisor. They claimed that they are "just a travel agency" and 2 of them rudely said that this was completely my fault and I should've prepared better. I will never book with Kiwi again, especially not after I just lost 1,000$.