Zincati has been around since the beginning of FCOS. Container based updates didn’t exist then, though OSTree based updates did. It is stable.
The benefits of Cincinnati+Zincati is that there is an Update Graph that is traversed (see Fedora CoreOS updates graph) when systems update. However, this architecture is more complicated for individuals to set up, because it requires a server that you have customized, stream and update metadata to be published etc… We are looking at making this easier in the future (i.e. making zincati client smarter and requiring no dynamic server, but rather a stored yaml/json file somewhere), but for now…
If you have a specific use case and control a fixed number of servers (i.e. you don’t have many different users with many different use cases) the much simpler thing to do is just build a container and put it in a registry and then keep those systems up to date based on that.