Do Rancher side products generally make it into a stable state such that you would want to run mission-critical systems on?
RKE (their Kubernetes deployment and management platform, mostly for various flavours of self managed environments) is pretty popular with the self-managed crowd that needs something to manage their on Orem Kubernetes clusters.
(Former employee) They tend to either get enough traction very quickly and be supported for years, or not and be abandoned in weeks/months.