Highly connected Cyber-Physical Systems (CPS) are central elements for the Digital Factory of Industry 4.0. The integration of existing automation infrastructure with cost-efficient laser systems for worker guidance creates Low-Cost Automation (LCA) CPS that enable quality workplaces. Such human centric LCA CPS must be usability optimized. This paper presents the findings of three case studies focusing on the perceived efficiency, effectiveness and system usability of an LCA CPS laser-assisted assembly station in a shop-floor scenario. By using an inductive approach, design principles are derived that enable usability optimized LCA CPS to support acceptance and productivity.