Terrible. Support does not work at all, they will reply to your complaint, but they will solve absolutely nothing. When you have a problem with them, they just defend themselves and won't admit their fault.
We had booked a ticket from Prague to Marrakech and back with transfers in Milan, i.e. 4 different flights. The carrier delayed one flight, so we didn't have time to transfer to the next connecting flight. Logically, we claimed this flight. However, the kiwi.com system works in such a way that you claim either all flights or none. So it happened that we only got a ridiculous amount back, because the other carriers quite logically did not want to return the money and the tickets were forfeited. If you don't like your refund then you're out of luck, kiwi.com doesn't care, they take it as solved and don't care anymore. NEVER MORE.