Both Redis cluster and redis-py-cluster is considered stable and production ready.
But this depends on what you are going to use clustering for. In the simple use cases with SET/GET and other single key functions there is not issues. If you require multi key functionality or pipelines then you must be very careful when developing because they work slightly different from the normal redis server.
If you require advance features like pubsub or scripting, this lib and redis do not handle that kind of use-cases very well. You either need to develop a custom solution yourself or use a non clustered redis server for that.
Finally, this lib itself is very stable and I know of at least 2 companies that use this in production with high loads and big cluster sizes.