Various assistive robots for supporting the activities of daily living have been developed. However, not many of these have been introduced into the market because they were found to be impractical in actual scenarios. In this paper, we report on the usability test results of an assistive robot designed for self-feeding for people having disabilities, which includes those having spinal cord injury, cerebral palsy, and traumatic brain injury. First, we present three versions of a novel self-feeding robot (KNRC self-feeding robot), which is suitable for use with Korean food, including sticky rice. These robots have been improved based on participatory action design over a period of three years. Next, we discuss the usability tests of the KNRC self-feeding robots. People with disabilities participated in comparative tests between the KNRC self-feeding robot and the commercialized product named My Spoon. The KNRC self-feeding robot showed positive results in relation to satisfaction and performance compared to the commercialized robot when users ate Korean food, including sticky rice.