I was very disappointed with Kiwi. First I had to pay a fee for booking with them. I have neer read that anywhere on their page - it must be somewhere in the very small paragraphs!
Then the e ticket said, that I have a flight, on which I can not check-in language. So I packed my hand language ( it had the right size and weight but American told me that my personnel item can not have wheels (!) So I had to check it in and pay 35 Dollars.
On my return flight, Kiwi did not inform me about a flight cancellation. I had to wait 9 hours in New York. Customer service told me, that they had not been informed by American, but when I called American they could tell me the exact day and time when they have sent the email to Kiwi (3 days prior to the flight!)
It was definitely the last time I have used Kiwi.