In order to use kinto you have to download it and host it on your own server infrastructure. While it does help you avoid outsourcing your data to a third-party, it also adds the overhead of having to maintain a backend for your app.
Kuzzle has no hosted version. In order to use it, you have to install it to a remote machine. This can be cost-effective but it also adds overhead because you will have to take care of the hosting and backend infrastructure yourself.