In the case of relatively small quantities, Urethane Casting Process is more economical process, while costs of both CNC and Injection Molding are much higher.
There are also some customized products only need dozens per year, one-time investment of silicone mold is a good option, such as large biochemical analyzers, spectrum analyzers, etc.
By using polyurethane materials, you can simulate the general properties of injection molding materials. For Some special requirements, like under-cut structure, soft plastic materials, or the customer need solid color plastic.