Would give minus stars if possible, in fact even the use of the word "stars" is misleading, with some sort of implication of something in any way positive.
I now finally have my money back, after a week back and forth with their "chat" (i.e. either bots or people born without a brain), over an hour long call and then finally taking to twitter and linked in. If they have taken your money for flights that don't exist, take to twitter and message their employees on linked in - only then will you get a response written by a helpful person...
Anyway, this is a long post, but if you are looking for a review when deciding where to book your flight, please do read this. You will definitely NOT use kiwi.com. So I booked a flight through their website, they took my payment and then once they had my money (almost a thousand UK pounds) they then emailed me saying actually the flight I had booked was not available any more. But they still had taken my money, and said it would be 10 days to get a refund. If you do not have spare money lying around to book another flight, do not use them, as if the booking doesn't go through you can't get your money back for 10 days. However, there was the option to have "kiwi credits" back immediately, and as I saw another flight I wanted on the website, I took the credits to book that instead. Then that one also turned out to be unavailable, even though yet again they took my credit money and the slight additional extra cost for the flight. I had to then book through another provider, as now kiwi.com weren't showing the flights I needed on the website (even though I knew they were available, and booked the exact same flight then through another provider, and I'd also checked the BA and Air NZ websites and seen they were available...). I then of course wanted a refund of my money, but as the second booking that hadn't processed either was in "kiwi credits" they said they were unable to refund the original payment card. Their chat function is ABYSMAL, do not expect to get any sort of response from anyone with a brain, went back and forth with them for a week, getting copy and paste irrelevant answers. Then they said I needed to call them. Was on the phone for over an hour, the person I was speaking to was doing his best to be helpful and kept checking things with his superiors - who kept then still saying no to the refund OF THE FLIGHT THAT THEY TOOK MY MONEY FOR BUT THEN DID NOT PROCESS. Finally, I took to twitter, tweeted them, and tweeted on every single one of their posts, responded to other people who were tweeting them about similar issues, even took to linked in messaging anyone listed as working at kiwi.com. Finally, after this, they have agreed to refund the booking, the booking that they took the money for then didn't complete, and kept the money.... Absolute disgrace. Never never never use this company. If I hadn't have kept following up down every avenue, they would have just kept my thousand pounds. Thieving scum.
Also, have seen lots of negative reviews go up recent on trip advisor, and they seem to have responded by adding lots of random positive reviews... take that how you will.