I only know of one flip phone sold in the U.S with KaiOS. I had one. It was a terrible flip phone. And I know flip phones. Like, the flip phone of 10 years ago did not give you a delay every time you pressed a button. The KaiOS one did. It also did not have installable 'apps' as was the original promise of KaiOS. It's UX was generally very confusing (yes, flip phones have a UX; you notice especially when it's a bad one).

I don't know if it's doing better in non-US markets. But I don't think so; someone else _did_ take the Firefox OS source code which of course had an open source license, and adopt it and rebrand it as KaiOS. I am not sure what their aspirations for it are. Currently, I do not think it is the promise of what people hoped FirefoxOS would be (and may or may not ever have been).